Think about it guys. Who was Kasparov's competition back then? Peter Leko? That guys rating is going down. Kasparov would barely make it in the top twenty with today's competition. Both Kasparov and Karpov are the product of their times, the pre computer era.
Who were they? Vishy was one of them. Vishy still is top 2-10.
Chess has evolved, but great players do adapt, and picks up the new stuff fast. I guess Morphy, if he stood up from the grave with the brainpower he had on top, would lost a lot in a few tournaments, but picked up ideas for every loss and after some months been up fighting close with Magnus, Vishy and the top 50.