Sampras had only two years in his career, 1993 and 1994, where he was a truly dominant #1 player, and even in those years he failed to win more than 2 Slam titles.
Sampras had a very one-dimensional game after 1996, and by the end of his career, other players on the tour were openly contemptuous of his inability to play from the baseline. At Roland Garros, Sampras was just another guy in the Top 100 struggling to win a couple of rounds.
While the crown jewel of Pete's career, his 7 Wimby titles, is nothing to sneeze at, you have to consider that out of the few occasions from 1992-2001 when he played a big serve-and-volley player who had an on day, three times he was beaten (Ivo in '92, Krajicek in '96, Feds in '01), and a fourth time (Philipoussis in '99), his opponent retired injured after winning the first set.
Two of the Pistol's USOpen victories against Agassi ('95 and '02)were due, plain and simple, to Agassi getting screwed by the idiot USTA schedulers forcing him to play late into Saturday night in his semifinal matches.
Borg skipped the Australian Open during his 9 year period of dominance. If Borg had bothered showing up in his prime he would have won the Australian four or five times, giving him 15 or 16 Slam titles, and people would have Borg ahead of the servebot.