For the sake of context, I think it's worth mentioning that none of the champions in this list faced either Sampras or Federer on their road to victory...
So?? Agassi faced Becker, Ivanisevic and McEnore. 3 Wimbledon champions. He also defeated other great grass-court players like Rafter and Krajicek at Wimbledon.
And Wimbledon is the only grass tournament that matters. There's not a single M1000 on grass and, of course, another slam on grass. You may say that Djokovic is a better clay-courter than Costa or Gaudio despite not winning Roland Garros because he has countless M1000 wins and finals there. But Wimbledon is pretty much the only big thing that is played on grass (unfortunately)