Most of those you rate ahead of Spassky in 73 finished behind him in the 73 USSR championship so your position seems odd to me .
Could Today's 2600 GMs All Beat Bobby Fischer?

http://graeme.50webs.com/chesschamps/ussr/ussr41.htm
A crosstable of the 73 USSR championship , note Tal even had a minus score .

You're basing EVERYTHING on a single tournament. There were other events in 1973.
Here are the official FIDE ratings for July 1973 and the end-of-year ratings:
July 1973 - FIDE Rating List
2. Karpov, Anatoly g URS : 2660
. . Tal, Mikhail N. g URS : 2660
4. Spassky, Boris V. g URS : 2655
5. Portisch, Lajos g HUN : 2650
. . Korchnoi, Viktor g URS : 2650
7. Petrosian, Tigran g URS : 2640
8. Botvinnik, Mikhail g URS : 2630
9. Polugaevsky, Lev g URS : 2625
10. Larsen, Bent g DEN : 2620
January 1974 - FIDE Rating List
2 . Karpov, Anatoly URS : 2700
3 . Korchnoi, Viktor URS : 2670
4 . Spassky, Boris V URS : 2650
5 . Portisch, Lajos HUN : 2645
6 . Petrosian, Tigran URS : 2640
7 . Tal, Mihail N URS : 2635
8 . Larsen, Bent DEN : 2630
9 . Polugaevsky, Lev URS : 2630
10 . Kavalek, Lubomir USA : 2625

The January 1975 list, which reflects the Candidates matches, is perhaps even more interesting:
January 1975 - FIDE Rating List
2 . Karpov,An. (USR) : 2705
3 . Kortchnoi,V. (SUI) : 2665
4 . Petrosian,T. (USR) : 2645
. . Polugaevsky,L. (USR) : 2645
. . Tal (USR) : 2645
7 . Portisch,L. (HUN) : 2635
8 . Larsen,B. (DEN) : 2625
. . Spassky,B. (USR) : 2625
10 . Huebner,R. (FRG) : 2615

To me its more meaningful/significant to finish ahead of your rivals in an event than it is to be 10 points higher rated on a rating list . On your 73 list there isnt even 50 points difference between #2 to #10 . Thats pretty insignificant imo . I base my view on practical results while you seem to base yours on rating lists .... It is clear however that Fischer was far ahead of the others .

So, by that logic, in 1974, Karpov and Korchnoi were miles ahead of Spassky. What happened between 1973 and 1974 that made Spassky so bad in comparison?

Ratings are more reliable measures of playing strength than a single tournament result. Matches are generally even better measures.

I think Spassky no longer had any ambition to be world champion after losing in 72 , thats what happened . Clearly both Korchnoi and Karpov had plenty of ambition . Spassky was very lazy , even he said so himself and I dont think he enjoyed the " burden " of being a soviet world champion . He was still a top player , when he wanted to be , for at least 10 years after losing in 72 though imo , regardless of what ratings lists say . As proof I offer his win of Linares in 83 ahead of reigning world champion Karpov .
I have studied Fischer's games for years. I got interested in chess during the Spassky match. Yes I have some mileage on me. Larry Evans published a book with a diagram and commentary for every move which I wore out.
As great as Fischer was it would take some time for him to get up to speed against 2700+ players in the openings. In 1972 the Scotch, Berlin, Petrov and Marshal and others were club openings. He would know nothing of the deeper theory discovered in the last 50 years. In the middle game and especially the end game he would hold his own.
I don't think he could dominate now like he did then even with the same access. There are far more strong players these days. Everyone has a 2700 computer to practice against every day. Before computers, the opportunity to hone your skill against tough opponents were much harder to come by. Today's player have training programs that accelerate learning. It is amazing that top players consistently play the top or one of the top computer moves. Bobby worked hard with limited tools and was truly great, but the best moves are the best moves, and now many top players find them.

Spassky's head-to-head record against Karpov is 2-14 with 23 draws. Ambition doesn't explain that sort of domination.
Yeah, I agree that Spassky was lazy. Spassky played some of the worst chess of his career in the first half of the match with Fischer. He didn't remember his lines, missed simple tactics, and just played poorly. He managed to play better in the second half of the match though.
Spassky has had a few good tournaments, but imagine someone arguing that Leko was better than Kasparov because he won the 2003 Linares tournament. It's a ridiculous argument because you cherry pick a single event and ignore the rest of the record.

The problem is that I am not arguing that Spassky was better than this or that player , only that in 73 he was still top 3 , which I stand by . Karpov's dominance over Spassky is indeed suspicious and may have something to do with Karpov being the " favored child " of soviet chess beginning in about 73 or 74 . Spassky was still receiving a "stipend " from the USSR even when living in France but when he finished ahead of Karpov in Linares 83 that was discontinued , he was punished even though he and Karpov drew their game . How dare he finish ahead of the chosen one in an important event ! Korchnoi got out to try and not be influenced by all the politics involved in chess for Soviet players .

Lola reveals her ignorance and hate everytime she posts anything about Fischer .
Bit harsh Reb!
TY Matthew....NM Reb and I go back quite a wayz. I don't want him to feel that I'm personally attacking BF 'cuz I'm not at all. In fact, if anyone attacks him personally ?....they will hear from me. Altho' I will proceed with much reservation if they -'ly comment about what he used to say about women as it related to their chessplaying skill.
All I am asking is that NM Reb keeps things in "objective perspective". He owes that to us ! And, one of my goals here is to do just that....be his reminder.
He's a magnanimous bugger, but I like him a lot. And IDK if he reciprocates, I still like him and I fully respect his FIDE title and his opinion....but boy are they strong !

Ratings are more reliable measures of playing strength than a single tournament result. Matches are generally even better measures.
....and that's exactly why BF's run in 1971-72 were an aberration. Believe me, he would've been brought down if he wouldn't have imposed it upon himself.
Okay. I'll just say it....
NM Reb has been trolled by BF & it has something to do w/ his youth. The rest of you need to be careful here. Pleez....tread w/ caution for your own sake ?

Why 2600 ? Fischer was 2785 in a time when he was the ONLY player over 2700 . 2600 was much harder to achieve in the 70s than it is today so 2600s today are likely weaker than 2600s in the 70s . Fischer would smash today's 2600s and probably the 2700s as well . Only those above 2750 today might give Fischer some problems , even so my money would be on Fischer until he faced those over 2800 ....
2600 mightve been harder to get to, but fischer was better than everyone in his time... isnt that how he got so high? He was able to achieve more wins. But playing against todays super gms, he surely would not win as many games and therefore the rating should be at least a little lower right?
... Spassky won the USSR championship in 1973 after losing to Fischer indicating that he was still one of the top 2 or 3 players in the world .
I'd rate Fischer #1, Karpov #2 Korchnoi #3, and Spassky battling it out with Petrosian and Tal for 4-6 in 1973. Chessmetrics has Spassky in tenth, behind even Polugaevsky and Geller in 1973. Leonid Stein was also ahead of Spassky until his untimely death in July, 1973.