I agree that Sampras wouldn't be quite the same monster with today's equipment (vs 1990's); however, his ability to go really BIG on any shot (2nd serve, FH, BH) would win him a lot of matches today. He matched the athleticism of today's top 3 guys (well maybe not Nadal), and he had the ability to serve you off the court (grass/hard). In addition, he seemed to possess that kind of steely nerve required to gut out tight matches on the big stage.
By contrast, I think Agassi would be less competitive with today's equipment... almost entirely due to his lack of athleticism. Further, the unique qualities (hitting early, hard, spin) that made him such a great player in the 1990's are the same qualities that many top players use today. He was everyone's idol, right?
The game is being owned (at the top) by taller & quicker players. Hard to believe the smaller & less-than-superfast guys will ever make it back to the top.