I sometimes think of this. Mac has 7 GS titles. He should have won the French in 84 (anyone who saw that match will remember how Lendl was outclassed during the first 3 sets), and Wimbledon in 80 and 82 (losses to Borg and Connors in 5-setters). Yes, I know that the "should have won" argument is subjective, and that he lost those matches, but Mac was clearly unlucky in these three finals, where he was the better player. That brings us to 10 GS. Let's assume he would have won the Australian (on grass) as many times as he won the US Open, and we're at 14 (all between 79 and 84).
I can't make the same argument for Mac post-85. Tatum, cocaine, and the advent of the modern game with modern racquets were too much for one volatile Mac to deal with. I still say that if players had to return to wood racquets tomorrow, Mac would be back in the top 10 right out of bed at 48 years old. Imagine Nadal with a Maxply Fort?
I know, I know, this is just nostalgia from an old man...