I disagree with this part of the post. Agassi might or might not have matched up well with Sampras, but it's not right to say the big servers were worse matchups for sampras than agassi.
Sampras has an excellent record against philipoussis, he is not a bad matchup at all for sampras. Sampras has a so-so record against Krajicek. Overall, once you abstract from any single big server matchup because small samples are always problematic, sampras did very well against the whole set of big servers (krajicek, phillipoussis, Ivanisevic, Rusedski, Becker). Sampras has a 44-22 record against this entire group.
In contrast, sampras has a 20-14 record against agassi. Even if you subset just to the GS, agassi does no worse than the big servers. This tells us that Agassi was the more dangerous opponent to sampras compared to the set of big servers. This is not only borne out in the overall w%, and the grandslam w% but also in the way that agassi played in some of his losses vs. sampras in grand slam matches. Agassi was certainly in the 1993 wimbledon and the 2001 and 2002 U.S. open matches, when sampras was playing at a good to high level. So even in 3 of out of his 6 losses versus sampras agassi put up a very good fight. In contrast, I can only think of 2 matches out of the 11 losses where the big servers put up a good fight (98 wimbledon for ivan. and the 2002 u.s. open for rusedski). The rest were generally straight forward affairs.
Let me quote from Pete's book on the various matchups he faced.
Most guys stayed away from Andre's best shot, but I wanted to get to it in order to get him moving. If I was able to hit my backhand deep and hard to his forehand, I could start doing damage because the flow of play almost demanded that he go crosscourt -- bringing one of my best weapons, the running forehand, into play. That gave Andre something to fret about, because I could make him move with my forehand, and he wasn't an exceptional mover.
I also sought to get into forehand rallies with Andre. Those were athletic hitting contests in which I felt I had an edge, however marginal. (242)
Needless to say the natural flow of play is Nadal's forehand going to Federer's backhand -- strength to weakness.
Sampras/Agassi had more strength-to-strength, such as in their forehand rallies; and of course Pete's serve went directly against Andre's service return. And if the court was sufficiently fast, Sampras had the edge in those contests, because it aided his serve and made his superior movement felt.
He also mentions how on grass Andre's shots, especially his second serve kickers, would sit up comfortably for him.
Obviously that wasn't the case with the big servers, and this is what he says about Krajicek:
I never really liked big servers, the guys who could do to me what I routinely did to them. Returning serve and hitting passing shots were not my strengths. I was okay with them, but having to do that over and over took me out of my comfort zone. Krajicek could really put the pressure on; if he had his serve going, he was very tough to break, and that put more pressure on my service games. (285)
The big question for me on every surface but clay was, "Okay, what do I do to break the guy?" That was because I always felt confident that I could hold my serve. Andre didn't have that luxury -- at least not to the same extent that I did. (241)
The thing that set Stich apart from all the rest, Pete thought, was his ability to hit his second serve well and consistently. He said that he judged opponents by the quality of their second serve. Yes, "big serving" bothered him, but to be more precise, what he felt was really threatening was someone whose second serve was consistent, accurate, not easy to attack. Because then Pete could continue holding, but "what do I do to break the guy?"
The Krajicek loss:
He was suddenly going for his shots, especially his second serve. Whether he knew it or not, he was taking me into territory I least liked to visit. My m.o. called for me to approach even the most lethal serve-and-volleyers with the expectation that I'll get a good look at some second serves. If that happened, I could beat them. The strategy worked against Goran Ivanisevic, it worked against Boris Becker, and it worked against Stefan Edberg. But when it became harder for me to sniff at a second serve, it created a chain reaction. If I couldn't get to his serve, that put more pressure on mine. I think Richard sensed that, and his own excellent serving freed up the rest of his game, especially his return games. And that's how it almost always works. (173)
And something similar happened in the Philippoussis match. I did my own stats on that match, and Mark's success on points started by his first serve was not terribly high, at 78% (lower than Pete's). But his success on second serve was way up at 73% (thirteen points higher than Pete's own number).
It was surprising in '96, when he was in his prime, that he lost in straight sets on fast surfaces to Krajicek and Philippoussis, though Pete's description of a "chain reaction" helps explain what kind of a hole he felt himself to be getting into, when someone else's strength (the serve, but particularly the second ball) started cranking up against what he felt was the weakest part of his game (returning and passing).
It's just about what your strengths and weakness are, and what the other guy's are.
What your pointing out is overall records, and I fully agree that Agassi had the best record against Sampras. But it wasn't because he had any advantage in the matchup of strokes. It was because he worked so hard, was mostly uninjured, decided to stick around for a long time and proved to have great longevity.
By Pete's own account, the big servers fell away for various reasons: Philippoussis due to injury and lack of dedication; Stich because he "didn't seem to enjoy life at the top"; Krajicek because mentally he ran hot and cold from week to week. That's the reason that you find them, more often than Agassi, losing to Sampras, and having fewer wins against him. But matchup wise, they had every advantage.
