FIDE's knockout tournaments were considered "unofficial" by many because it didn't follow the classical championship lineage. Those that won their WCh title through these tournaments, while no doubt being great players, had no staying power - except for Anand and Topalov. Consider: Ponomariov peaked at world #6 and has a high of 2764, now rated 2683; Khalifman peaked at #12 and 2702, now 2615; Kasimdzhanov #11 2715, now 2676. Granted, there's been several years between then and now, but look at Kramnik, Anand and even Topalov, who was #1 for a good while at 2816 until overcome by none other than Carlsen but is still #15 at 2749. The reason those FIDE World Champions are considered "second-rate" by so many is because they are not held as truly great players - something that EVERY classical world champion has been. With the exception of Fischer, every world champion has played at the very top level for years and years, whether they still held the title or not. Ponomariov, Khalifman and Kasimdzhanov got lucky. So did Topalov, even though he WAS dominant later in his career. No one denies that any of them were strong players. They just weren't "true" world champions.
FIDE champions vs Vladimir Kramnik (during Kramnik's reign)

FIDE's knockout tournaments were considered "unofficial" by many because it didn't follow the classical championship lineage. Those that won their WCh title through these tournaments, while no doubt being great players, had no staying power - except for Anand and Topalov. Consider: Ponomariov peaked at world #6 and has a high of 2764, now rated 2683; Khalifman peaked at #12 and 2702, now 2615; Kasimdzhanov #11 2715, now 2676. Granted, there's been several years between then and now, but look at Kramnik, Anand and even Topalov, who was #1 for a good while at 2816 until overcome by none other than Carlsen but is still #15 at 2749. The reason those FIDE World Champions are considered "second-rate" by so many is because they are not held as truly great players - something that EVERY classical world champion has been. With the exception of Fischer, every world champion has played at the very top level for years and years, whether they still held the title or not. Ponomariov, Khalifman and Kasimdzhanov got lucky. So did Topalov, even though he WAS dominant later in his career. No one denies that any of them were strong players. They just weren't "true" world champions.
World Championship does not require to stay on power after you obtain it, one must win it through a system that allows WORLD to participate in it. FIDE's system was available for everyone who can participate, you or me or Ponomariov. Ponomariov, Kasimjanov or any of them qualified there and won it. On the other hand, after Anand's 1995 match only 3 players at most had a chance to challenge Kasparov: Anand, Kramnik and Shirov. How is that a world championship when only 3 people had a chance to play for championship? And those 3 were not selected with qualifications either, on the other hand to qualify to FIDE championship there was a cycle everyone had to go through. You have to play in your national championship, then earn right to play via interzonals and etc.
Coming back to the strength of those FIDE champions, as shown above they were either equal to or behind only with a slight margin that "classical" champion. Their career performance might have been lesser than Kramnik but when they faced that Classical champion during that champion's reign they were not inferior. Khalifman was losing by 1 game and Topalov by 2 games. Per performance they were as worthy as Kramnik was and by credentials they were more worthy than Kramnik: Kramnik's title shot and championship came due to a luck and that luck's odds were 33% at most since only Shirov, Anand and Kramnik were eligible to play fot it. Kasparov himself selected Shirov and Kramnik to have a match to decide a challenger for him, then it collapsed and he contacted Anand and after even this failed he went to Kramnik.
FIDE's system, no matter how "joke" was this, was more a world championship system than those "classical" claimants were playing in.
Up until 1995 Kasparov - Anand match classical line had a point but they lost that point after they failed to organize a world championship system.
We can dismiss Ponomariov or Kasimdzhanov in career comparison with Kramnik but we can not do so when it is to judge their championships. Kramnik, no matter how excellent chess player he was, became champion in a system that was not even a joke. Reminds me of Alekhine cherry-picking his own challengers.
Don't misunderstand, I'm not arguing that the "classical" championship lineage was perfect and especially not during the PCA period, far from it. I was merely explaining why, IMHO, many dismissed those FIDE knockout championships. I vividly remember when Ponomariov won in 2002 as well as him trying to live up to his title in tournament play following his ascension. He was only 18 when he beat Ivanchuk to claim the title and for a while in 1998 or 1999, he was the youngest GM in history. IIRC, immediately following the WCh he won he placed second at Linares trailing only Kasparov. Like I said, no one denies that those who won the WCh in that period were strong players. Only that they aren't and weren't as strong as the likes of Kasparov, Karpov, Kramnik, Anand, Carlsen, etc and therefore many do not consider them true champs. The main point that I would raise is that with the likes of Kasparov or Kramnik, we say former World Champion, period. But with Ruslan, Khalifman and the like, it will always be former FIDE world champion. That 13 years was a bit troubled for the elite players and the title of "FIDE World Champion" from that time will always, to very many chess fans, have a negative connotation. I don't argue that Kramnik was just as lucky with his title shot. Difference is, IMO, he rose to the challenge and won, then proceeded to assert himself for years afterwards even to this day. I still wish that Shirov would have gotten his shot, though I'm sure he would have lost. I was a huge fan of his and still am.

Don't misunderstand, I'm not arguing that the "classical" championship lineage was perfect and especially not during the PCA period, far from it. I was merely explaining why, IMHO, many dismissed those FIDE knockout championships. I vividly remember when Ponomariov won in 2002 as well as him trying to live up to his title in tournament play following his ascension. He was only 18 when he beat Ivanchuk to claim the title and for a while in 1998 or 1999, he was the youngest GM in history. IIRC, immediately following the WCh he won he placed second at Linares trailing only Kasparov. Like I said, no one denies that those who won the WCh in that period were strong players. Only that they aren't and weren't as strong as the likes of Kasparov, Karpov, Kramnik, Anand, Carlsen, etc and therefore many do not consider them true champs. The main point that I would raise is that with the likes of Kasparov or Kramnik, we say former World Champion, period. But with Ruslan, Khalifman and the like, it will always be former FIDE world champion. That 13 years was a bit troubled for the elite players and the title of "FIDE World Champion" from that time will always, to very many chess fans, have a negative connotation. I don't argue that Kramnik was just as lucky with his title shot. Difference is, IMO, he rose to the challenge and won, then proceeded to assert himself for years afterwards even to this day. I still wish that Shirov would have gotten his shot, though I'm sure he would have lost. I was a huge fan of his and still am.
Ok, did not misunderstand. I did not reckon you saying Kasparov's system was perfect or better.
The reason I touched their system is they should be viewed as undeserving champions who happened to win it. Kasparov won it in the world championship system and went undefeated but Kramnik did not win it in a "world championship system." Rather, he was just lucky to be even a challenger. I do not mean he could not have achieved challenger status, maybe he could and he probably could but he became a challenger due to luck.
If anyone is to be considered a former "lucky" champion, that is Kramnik no matter how good he was. His championship was won halfly by luck. That is why Kramnik should be referred with a special name before his title.
If one of these two systems were to be recognized as world championship, it has to be FIDE's. The other one was not even a joke after 1995. As thus, Khalifman - Anand - Ponomariov - Kasimdzhanov should be view world champions of that era, not Kramnik.

There's a very good argument to be made that the old "lineal" championship is an outdated concept. In almost every other sport, there is a new season every year and a new champion at the end of that year. Every football (soccer or American) team has to win the title next season is it wants to remain champion. Even in individual sports like tennis or golf, the Wimbleton or British Open champion has to win it all over again next year, or there will be a new champion. Why should the world chess championship be different?
hmm, it seems difficult to organize annual world chess championship with its current system. But still we can have a league like that of football. Imagine 30 or so chess players facing each other twice a year and thus selecting the champion.
Btw, WORLD championship is not annual in other sports or team sports at least. Football's WORLD championship is held once at every 4 years, so is basketball's.
National championships? It is annual in chess as well. There are more differences: Football's club championships are annual, national teams' are not. There is no such distinction in chess, no club and national championships. It is all individuals.

Meh, that just shows you that Kramnik wasn't a deserving world champ.
He fluke-won over Kasparov then refused a rematch. Big deal. He lost the title the very next match.
I do not consider his win a fluke but him having chance for world championship? I consider that a fluke since 1) He did not qualify through any system 2) He was just one of the 2 cherry-picked ones to have a candidates match to decide the challenger for Kasparov and he lost that yet Shirov's (winner of that match) title shot match were not finalized 3) Anand somehow rejected the match offer. Only after these 3 'lucks' Kramnik had a chance to play for world championship.
You demonstrate you are deserving champion by qualifying there and defeating the champion, Kramnik defeated the champion but he was there due to luck. His status is debatable but not that of 5 actual champions who reached there through qualifying a recognized, publicly known, agreed-upon and available for all system.

Oh yeah, I forgot about how Shirov got screwed at that time.
Anyway wasn't Kasparov going through a divorce at the time of the match, so he wasn't focused? Or was that a silly rumor I heard?
And as for people like Kasimdzhanov, he's never even been in the top 10. I don't care if FIDE gave it to him, the title is meaningless if you're not even in the top 10.
I do not know about Kasparov's divorce speculation.
FIDE has not given anythhing to Kasimdzhanov, he has taken it, he has obtained it, he has earned it and he has won it. HE CLAIMED IT SUCCESFULLY.
Many people scorn or underrate FIDE champions as someone who did not deserve yet somehow ended up becoming a world champion. I am gonna counter this views after I present their statistical results. FIDE champions after Karpov were Khalifman, Ponomariov, Kasimdhzanov, Anand and Topalov.
1. Khalifman vs Kramnik during 2000 - 2008
According to chessgames.com, in classical games Khalifman faced Kramnik 5 times during Kramnik's reign. Khalifman lost 1 game and drew the other 4. Enough to say Kramnik demonstrated superiority? Source: http://www.chessgames.com/perl/ezsearch.pl?search=khalifman+vs+kramnik Hardly sufficient but still Kramnik has the edge.
2. Anand vs Kramnik:
According to chessgames.com, after 2000 till Anand - Kramnik World championship match Anand beat Kramnik 4 to 3 with 10s of games being drawn. Note that Rapid matches, blitz matches and blindfold matches are not taken into account. Their head - to - head championship match are not included here, Anand won that match.
Like Khalifman's case, their head to head encounters here or there are not sufficient to conclude who was superior. In the match that mattered, Anand defeated Kramnik.
3. Ponomariov vs Kramnik: Classical games: 2 - 2. 2 wins for each and 6 draws. Equal. It is also according to chessgames.com
4. Kasimdhznov vs Kramnik: No known classical encounter during Kramnik's reign. They faced in blitz twice and both games were drawn. Insufficient data for conclusion.
5. Topalov vs Kramnik: After Kramnik's reign began and till their world championship match Kramnik defeated Topalov 4 times and lost to Topalov twice. 4 - 2. It does not include blindfold games, rapid and blitz games. Kramnik also won their dramatic match. I think it is enough to say Kramnik demonstrated superiority. Including the match their score was 9 - 7 with many draws.
Out of those 5 "undeserving" champions only 1 of them can be claimed to be shown to be inferior to Kramnik. Even that one's results do not have such margin, only 2 wins set them apart.
These 5 champions became world champion in a system that was known by everyone, that was recognised by authority and it was not their fault if Kasparov or someone else did not take place in it. And the absence of Kasparov or someone else does not get any credit from their success.They won it by defeating those who opposed them. Their title shot came due to agreed-upon and recognised system (even though it was controversial), on the other hand Kramnik's title shot came due to luck. If someone was an undeserving champion, that must be not one of the 5 FIDE champions, it must be Kramnik. I do not mean Kramnik was just a random person on the street who became champion due to random fluke, what I mean is Kramnik did not reach the zenith on his own, rather the zenith was brought to him and he seized this moment. Defeating Kasparov in 2000 was not an easy task, Kramnik deserves congratulations for this achievement.