Matter manipulation, energy manipulation, super speed, super strength: if it's a superpower then Thanos has probably had it at some point. Capable of surviving the destruction of entire planets and likely even blowing a few up by himself, Thanos has defeated the entirety of The Avengers, Hulk included, in the past. Usually stopped from doing any lasting damage by his own hubris, Thanos is nonetheless bigger, badder and certainly stronger than anyone that Earth could throw at him, let alone Earth's Mightiest Heroes. In a knock-down, drag-out fight with no stakes beyond who gets to claim the title? Yeah, The Hulk's going down hard.