Hall of Fame
Subjectively, an argument can be made for that winning more evenly in the four slams is more impressive than dominating just one and winning the others to a much lesser degree. Problem is, this can be argued the exact opposite way round. Why is it not more impressive to dominate one of the slams in a degree no man ever has before and still do reasonably well in the others? It's just as subjectively reasonable to say that a player who can dominate at one slam is more impressive than being fairly great in all 4 slams, but outstanding in none. It's an argument of versatility vs otherworldy domination. I would not consider Nadal a better/greater player had he lost 5 of his FO's to Djokovic/Federer and gained 5 slams elsewhere. He'd have a more 'balanced' resume, and be a more 'balanced' player, but by no means be a 'better' or 'greater' player because he still has won the same amount of titles. In fact, you could argue his peak level would be lower, because he could not dominate anywhere.