Nadal played both prime Federer and prime Djokovic for all of his career though, so that compensates for the 63% slams being clay. Actually, Djokovic is 59% HC slams and Federer is 55% HC slams.
Federer got a good amount before Nadal hit his prime, but it was like 6-7 (till 2006), not like full on running rough shot on weak players. He also had the misfortune of dealing with prime Djokovic after dealing with prime Nadal.
Djoko seems to have gotten the easy end of the stick between the 3 TBH (a large part due to his own longevity and mental fortitude). All I'm saying is that it's disgustingly easy these days for him.