Fed's style is effective/efficient which he only needed to be on 3rd gear. So what if he's been consistently at the top for all these years. He doesn't allow his body to breakdown the way Rafa must sacrifice to be at the top. Rafa required to be on 5th gear all the time, of course the wear and tear catches up rapidly. Also Nadal was already abusing his body at the very young age.
Tier1(goat): Federer; Tier 1.5: Laver, Sampras, Nadal, Borg;
Tier 2: Lendl, Connors, Rosewall; Tier 2.5: McEnroe, Agassi