The Fischer that Tal played was still a boy, not the giant who stomped the world's best with ease in the 70's. Over all game scores can be misleading, especially when one was an adult at their peak against a child. A great example of this is how Anand has a good score vs. Carlsen, but most of these were against a teen. The score is much more in Carlsen's favor if we just look at the last few years.
At their respective peaks, Tal, Kasparov, and Karpov did not dominate their opponents the same way Fischer did. Carlsen does not, but give the boy some time.
I believe that the reason why Fischer is undervalued as a chess player is because he simply didn't play in tournaments and championships as often as Kasparov. But the fact that Kasparov did more great things than Fischer does not make him a better player
Since the two didn't play each other, the only way we have to judge who was the better player is to compare their achievements, and for me 20+ years of excellence at the highest level far and away trumps Fischer's stop-start-stop career...there's just not enough data
Nobody undervalues Fischer as a chess player. If anything, people undervalue Kasparov...his rise was no less mercurial than Fischer's, and once at the top he proved he had what it took to stay there
Also, there's some Korean guy with an IQ over 200. Is he a better chess player than both Kasparov and Fischer?
I thought the limit was 200 for the IQ. I've checked the site which shows that and I think it's fake: it shows Kapsarov at 190, when he was tested in Germany and the result was 135. People like to blow things out of proportions.