The other thing about the Nadal and Federer rivalry is that when Nadal first faced Federer on grass at Wimbledon, he did win a set and was serving for another set so it wasn't exactly a slaughter although Federer won comfortably. Nadal was much more inexperienced on grass and a lesser player than he is now.
Agreed that Nadal was a lesser player in '06. But I think that can be exaggerated when looking at grass. The '06 Wimbledon was Nadal's third. Borg was in his fourth Wimbledon when he won it for the first time; and despite his relative youth he thoroughly dominated the tournament as you know, not dropping a set.
I do think on the old grass, against SVers, maybe Nadal would have had a harder time adapting (though I think he would have done it). But on this higher bouncing grass, facing mostly baseliners, he seems almost a natural. I know, I remember, Nadal making the Wimbledon final in '06 was thought to be a fluke, and many people doubted he would make another. But in the '06 tournament he held serve 80 consecutive times, which is one of the best streaks at Wimbledon (Sampras had streaks of 118 and 97; Federer had one of 105).
And Nadal did not have a great serve; he wasn't getting by on his serve like Karlovic. Obviously if he could back up his (average) serve that well, you'd have to say his whole game was very well suited, or well adapted, to grass even in '06. You can't post that kind of streak through mere luck. You'd have to be already a fine grasscourt player (or else have Karlovic's serve).
So how do you measure how a Nadal at the peak of his powers would do against a Federer at the peak of his powers on grass?
Well it becomes so tricky because there's ultimately nothing to check against, since the matches will never take place. But I think you can say, this player's level of play, judged directly on its own merits, was this high, or this low. And then compare it against another player's peak performances. Ultimately that's still largely subjective but it can be done.
