Agassi met Sampras only twice at Wimb. Sampras wasn't his only roadblock at Wimb. I mean during 1994-1998, Agassi was nowhere to be seen against Sampras.
Federer is a much better player than Agassi ever was. He would have beaten Sampras at Wimb, unlike Agassi. The reverse of your argument can also be applied: that Sampras never had a player like prime Fed at Wimb to contend with.
I included Sampras as one of those with the weakest competition though.
Of course Agassi isnt as good as Sampras or Federer, and that is why had such a tough task facing Sampras, a clearly superior player especialy on faster courts, who was also a bad match up for him to boot. Sampras beat Agassi twice at Wimbledon and 4 times at the U.S Open and analyzing the draws Agassi would have been the likely winner of all 6, and at worst won 4 or 5 of the 6. At the very least his U.S Open would be WAY better and absolutely legendary without Sampras. It is hard to see him losing any of the 95, 2000, 2001 U.S Opens, 1990 is debateable. He also faced numerous surface specialists on clay, grass, carpet, as someone who clearly was at their best on hard courts, and still managed to contend and win something big on each on those surfaces. That is why I credit him as atleast having respectable competition, and moreso than Sampras who for him had a weak era to stay #1 and win at Wimbledon especialy. It isnt me saying Agassi is better than Sampras, but he had it tougher competition wise, in part since he is a weaker player to begin with and doesnt have quite enough game to beat form Sampras on fast courts in a big match.