zagor
Bionic Poster
Nadal's period of peak/dominance coincided with several downsides. He started off as a predominantly clay court player who took some time to start winning slams on other surfaces, was more injury prone than Fed (and if people want to credit Fed's game and genetics in this case, then so be it), and also had to contend with a rising and then very dominant Djokovic. Fed during his peak only had Nadal as his nemesis.
Novak beat Nadal 4 times in slams compared to 9 times for Fed. Neither Djokovic nor Fed are the reason Nadal didn't have an extended period of dominance. That's down to his inconsistency against the field off clay (if you want to credit Nadal's injures for that, then so be it), he doesn't even make it to those two on HC/grass unless he's zoning and playing way above his average level.
As for downsides, Fed had the one of having to face off against two 5 year younger ATGs in the 2nd half of his career, Nadal had faced zero resistance from the younger players and just recently got a YE#1 against a 36 year old player incapable of playing a full schedule and won a USO title without facing a top 25 player.
Also, Fed and Novak are two of the greatest HC players of all time which cut into both of their winnings on the surface. Nadal didn't have to face an ATG who has clay as his favourite surface (of course, the same goes for Fed on grass).