Its similar to Shaq. He just so insanely gifted, both physically (hand eye coordination) and skill-wise that he's impossible to guard and referee.
He also has an incredible understanding of the nuance of unwritten rules in the game. Like the whole push-off thing. Everyone is allowed to pushoff (Mitchell does it all the time on his drives in a much more egregious fashion than Harden does tbh) *to an extent*. It isn't neatly defined, but everyone knows you can't fully extend your arm, but you can kind of extend it. Harden has found that point and just abuses it because of how strong he is.
