We should all go back to what the creator, Stan Lee thought of Thor.
"How do I make a superhero stronger than anyone? I know, I'll make him a god."
Thus, Thor was born.
So, in Stan Lee's eyes and mind, no superhero could be more powerful than Thor.
Until of course, the writers made Hulk something he never was, nor intended to be.
Both Thor, and Supes would whoop up on Hulk.