They were so good back then that a kid like Chang could win a GS title. That would be impossible now because these guys would eat him for breakfast. The question should be asked other way around. How many of those guys would be as good today? What are the chances of Becker winning 2 AO in era of Roger, Rafa and Novak? You can ask the same question for any other GS.
Err… the game, equipment and training methods evolve. You can't just single out Change. Put Laver, Borg, Connors and McEnroe in the current era and they'd get eaten for breakfast.