That's a little short sighted. Ever since Nadal started his dominance as the clay GOAT Federer established himself as the indisputed #2 on clay (debatable now with Djokovic's arrival). I don't think you can say the same for Nadal on hard court or grass.
What your stats answers is: Who is more dominant on their respective surfaces, Federer or Nadal? The answer is obviously Nadal but that doesn't make him a more well player.