And again, like I said... look how many times Rafa beat peak Fed... yet none of them would argue his case? Smells fishy to me.
Well most people would agree that Nadal, while certainly a GOAT candidate, is not necessarily one of the best when looking at peak play. Besides on clay, peak Nadal doesn't usually hit unplayable levels like Fed/Sampras types can.
This is because Nadal plays disruptive tennis. His style is preventing the opponent from executing their game. When the rally is neutral, Nadal's topsin-heavy Forehand makes it difficult for opponents to start an attack. Then when the opponent is playing attacking, Nadal defends till he finds the right moment for a passing shot.
So Nadal usually doesn't blast players off the court, which is why his peak isn't "unplayable", rather he makes it near impossible for his opponents to play their game. Yes he usually beat peak Fed, but because Fed's game has an exploitable flaw (backhand). When Nadal is put up against a player without an exploitable hole such as Djokovic, then Nadal's peak play does not quite match his peak play.
The simplest evidence of this is that when Nadal runs into a big hitter who is playing their best tennis, then his disruptive tactics don't always work. His topspin FH gets blasted back at him and he's pushed around on defense till he loses the point. Examples are Tsonga AO '08, Soderling FO '09, Del Po USO '09, Rosol Wimby '12. Nadal has difficulty dealing with opponents who are painting the lines because he can't respond with tennis of that caliber, he specializes in making sure his opponents dont get to go for winners. Federer or even Djokovic can respond to this level of tennis with their own offense, which is why they hold their own against big hitters.
However, Nadal is possibly the best at maintaining a high level throughout a match, which is why he still leads a H2H with everyone. He's more consistent over the course of a match. So lets say Djokovic can hit a peak level of 10 and Nadal can hit a peak level of 9. If both are playing peak, Djokovic will likely win. However, Nadal still gets more wins because even when Nadal is playing poorly, he has a higher margin for error and is disrupting the opponent's game. So in a match, Nadal may not be playing his best but still be playing at an 8, whereas Djokovic could drop to a 6 or 7. Not bashing Nadal, this just the way that he plays the game and its highly effective most of the time!