But look at Becker, Sampras, etc, well after Lendl, they were hitting as hard or harder than most now, serve wise, they don't have the top spin of Federer, yet the guys today are far more ripped, except for Federer. Federer looks like a tennis player. He would fit in anytime from Connors forward. Same with Agassi, and he did have great endurance. The guys today are much more chiseled. Not huge muscle size outside of a few years where Nadal was suddenly great on grass and hard courts, I mean you can find pics of Djoko, even Murray, where every single tiny muscle in their upper body is well defined. You might believe they are competing at crossfit, but not tennis. I don't think it was working out smarter that did this. I think Federer was so far ahead of all of them, that they had to PED to have a chance, starting with Nadal, and then you had two guys dominating the rest, so they had to ped to get back competitive.
I'm not saying Nadal wouldn't have won every French open he did without roids. That slow surface and his natural speed was enough, but I don't think he would have won half as many anywhere else, if any.
Bigger size as far as height, is more to do with the change in style of the game. Once wood frames went poof it became a power game. No need to be small and fast, just big and bomb any shot you happen to be able to get to.