Kasimdzhanov can always take solace in having the longest surname of any world chess champion - by a clear 2 letters. He is beaten on the female side by Gaprindashvili, though.
who is the worst world champion of all time

It’s hard to say who the worst world champion was, so I’ll make it about who was the rudest and who had the worst beliefs. I probably don’t even have to say it because most of you already know who it is. Bobby Fischer. In my opinion, he’s the best chess player in existence, but not a very good human. He said extremely controversial, prejudicial things that made a lot of people hate him. There’s even a joke, never ask a man his salary, never ask a woman her weight, and never ask Bobby Fischer anything.

He only got into the candidates due to Karjaken's disqualification...
hmm, i'm not qualified to comment much, but i think this particular point you brought up isn't quite fair....being in China with the covid restrictions, he was unable to participate in a lot of tournaments at the time, which isn't his fault

Ding liren
nepo was obviously better than him and was typically leading the games and ding only won because of the mental stress both of them had and nepo cracked first

Well, the most logical answer here is Steinitz, as he was the first and played against players who were about 2100 in most of his games..

Ding liren
nepo was obviously better than him and was typically leading the games and ding only won because of the mental stress both of them had and nepo cracked first
Ding would smoke any pre Karpov world champion in a match

To be entirely honest, at the moment it's Ding. It depends on how the rest of his career goes but if we're talking about who it is right at this moment, it's Ding. He only got into the candidates due to Karjaken's disqualification and then didn't win the candidates, only getting a crack at the WCC because of Magnus's forfeit. He did not dominate the match with Nepo either with it ending in a tiebreak win after Nepo leading Ding for most of the match. He's only got a handful of other minor achievements (when compared to other champions) like winning the Sinquefield cup and being Chinese champion a few times. I really like Ding, but I think he's going to go down in history as the worst WCC but it depends on what happens. If he goes on to defend the title a few times this will not be the case. With the strength of the field however, this is a tall task.
Ding is literally a modern super grandmaster armed with stockfish, alpha zero, ect. To study. He would easily win against any world champion who was WC before Karpov in a match, and would most likely beat prime Karpov in a match too. Modern Super GMs are a different gravy

”It's only because of him that this upcoming match between two truly great players will be seen as less than legitimate”
It’s only because of him anyone is interested in a match between Nepo and Ding :-) At least few would care much about the result if the match wasn’t for the World Championship, and it can obviously only be for the World Championship without Carlsen.
But in general title matches attract more interest if they are between two even more truly great players than these. For title match participants in their 30s their careers can’t really be compared to those of players like Carlsen, Anand, Kramnik, Kasparov, Karpov, Fischer etc.
Nepo has been top 10 for only three years, and Ding has won very few tournaments, and didn’t even qualify for the Candidates this time, even if he got a spot after Karjakin was banned. In Tata he scored +1-3=9, and Nepo is probably going to score a result that is usual for him in the ongoing Düsseldorf tournament where he is a full point behind Aronian after three rounds. Nepo and Ding are very strong players, but it’s hardly Carlsen’s fault that they are not the general level of World Champions achievement wise.
A World Championship match should be played by the two strongest players in the world but FIDE has decided otherwise (and not for the first time...).

A World Championship match should be played by the two strongest players in the world but FIDE has decided otherwise (and not for the first time...).
FIDE held its usual qualifying events and Nepomniachtchi won (again) the right to challenge Magnus Carlsen. Carsen decided he wasn't up to going through all the preparation needed to get into top form, so he resigned the title. Not FIDE's idea.

A World Championship match should be played by the two strongest players in the world but FIDE has decided otherwise (and not for the first time...).
FIDE held its usual qualifying events and Nepomniachtchi won (again) the right to challenge Magnus Carlsen. Carsen decided he wasn't up going through all the preparation needed to get into top form, so he resigned the title. Not FIDE's idea.
Well, if the defending champion does not defend, they could (and probably should) have awarded the title to the challenger (Nepo), just like they did in 1975. So it was FIDE's decision.
Of course the statement that "should be played by the two strongest players in the world" is just nonsense. Instead, it should be between the champion (whoever it is) and the challenger who fought his (or her) way to get there.

other than those random fide pca world championship split world champions in that era who 98% of people don’t know about, def euwe

A World Championship match should be played by the two strongest players in the world but FIDE has decided otherwise (and not for the first time...).
FIDE held its usual qualifying events and Nepomniachtchi won (again) the right to challenge Magnus Carlsen. Carsen decided he wasn't up going through all the preparation needed to get into top form, so he resigned the title. Not FIDE's idea.
Well, if the defending champion does not defend, they could (and probably should) have awarded the title to the challenger (Nepo), just like they did in 1975. So it was FIDE's decision.
The difference is that in 1975 the challenger was determined by interzonal tournaments that produced eight finalists, then four matches reduced that to four players, two matches left Karpov and Korchnoi, who played a 24-game match. When Fischer later refused to play the world championship final match, the two top challengers had already played a match so Karpov didn't need to win another match vs Korchnoi.
The standard answer to this question is Euwe, but it is still worth taking a look at the tournaments he played as World Champion. It’s not as if he was all that bad, and far from sure for example Ding Liren will do better in that respect. Euwe also won the title by beating Alekhine, which was impressive enough. And, as can be seen below, he did better than Alekhine also in the tournaments they played after the match:
THE ROOOOOOOOOK