Pete Sampras, in his prime, possessed more weaponry than any player in the history of the sport. While he wasn't a dominant returner, he didn't have to be. His serve allowed him to bide his time and conserve energy. And he could raise his level of play at critical moments in matches both on serve and when returning.
And I strongly believe that when Sampras played to the peak of his skills, there has never been a player who could match him. He was wickedly talented and mentally tough as nails. Only his chronic physical issues (bad knees, thalassemia minor) prevented him from being more dominant than he was. Despite these issues, he ruled the tennis world with an iron hand and ruled Wimbledon like no one ever had before him in an era of big servers and strong serve and volleyers (Edberg, Rafter, Becker, Krajicek, Ivanisevic, Stich). His 8 US Open final appearances over a 12 year period is a tribute to the talent of the man. He could do it all. While it may be true that the missing French Open title is a blemish, this "hole" in Sampras' resume is more of a testament to the strength of the clay courters in his era than any kind of fault in his game. Andre Agassi, who arguably had the some of the best groundstrokes in the history of men's tennis, only won in Paris once. Winning in Paris is a crapshoot when half the population of Spain can win at Roland Garros on any given year.
But, grass and hardcourts are the great equalizer. These surfaces require creativity and brilliant shotmaking. And these were the surfaces where Sampras was most dangerous. On these surfaces, it's eat or be eaten. And Sampras rarely went home hungry.