Karpov is of a much safe positional player than either Kaspa or Fischer. The latter players could also thrive in chaotic positions and win them, a style of play that really excites casual and critical observers. Nakakabuhay ng dugo, sabi, introducing the element of controlled confusion in the board. Karpov's classical training is against that, though he showed some flashes of the same in his lengthy battles with Kaspa.
There's also that controversial ruling in Kaspa and Karpov's championship match where rules were changed just when Karpov was leading by some margin. This is probably one of the reasons people take Karpov as the greatest rather than Kasparov.
I don't have the exact figures of number of games, but lifetime head-to-head comparisons of any two players should only matter if they had played each other under a championship run or the like, much the same way we do now with Kasparov and Karpov after their legendary championship games. The stats could be skewed by a number of factors if we don't do this. For example, peak Korchnoi scored a number of wins against a youngish Fischer, as did Tal I think, something that would be in doubt in a titular event and for a lengthy continuous number of games at the height of Fischer's ascendancy later on.
The controversy regarding the rating tweaking received critics from many sectors way back, but FIDE stood its ground. It should make for an interesting read for those who are seriously drawn to this topic. There was a claim then, for example, that FIDE intentionally gave too much ways for a player to achieve higher rating despite the relative lower strength of the event, so on and so forth.
Going back to the ratings, I recall that chess then was viewed as almost an extension of the Cold War between the former USSR and the US. Chess at the time was shrouded in heavy international politics and intrigue, and the rating move was viewed as sheer manipulation spearheaded by USSR honchos bent on proving that USSR players rank supreme in the chess world. It was such that the US declared it a national holiday when Fischer took the crown from Spasski, a first for the nation and against its mortal enemy no less.
