According to the comics, Hulk as no upper limit to his strength and it's his rage the allows him to tap into more than he would normally have. He just has to get pissed enough and he can beat the dog shit out of Thanos even with the power stone.
You gotta remember everyone in the movies is nerfed and they are no where near their comic freats of strength level....

So there's that
 
Just realized that Thanos had the power Stone when he gave hulk the beats.... And the power Stone makes you the strongest in the universe.

Hulk gonna run that back when he ain't got his glove

The stones don't automatically enhance people like in the comics. Thanos had to activate them to use their powers. He didn't do that against Hulk. You could tell because it wasn't glowing.
 
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The stones don't automatically enhance people like in the comics. Thanos had to activate them to use their powers. He didn't do that against Hulk. You could tell because it wasn't glowing.

The Russos have confirmed this as well.