I’ve watched the Hulk/Thanos fight several times and it just seems there is something wrong with the Hulk. I can’t put my finger on it, but it just seems as if the Hulk is not his Hulking self. That he won’t come out later in the movie indicates there is something wrong. But I don’t think it has anything to do with being beaten by Thanos. It’s something going back a little farther.
Nor do I buy into the speculation that Loki is actually pretending to be Bruce Banner/Hulk. How, exactly, would that not be noticed by Dr. Strange – Master of the Mystic Arts? In “Thor – Ragnarok” Dr. Strange is able to sense Loki’s presence on Earth without even being in his presence. You think he’s not going to sense him from at less than 5 feet away? Exactly.
Anyway, I think the problem is that Bruce is no longer “always angry.” The Hulk will only come out when Bruce is angry. So my guess is that when Bruce finally gets angry again, Hulk comes out a hell of a lot more powerful than when he first took on Thanos.
Of course, like all the other posts on the internet about this subject, this is all just speculation. And I’m pretty sure I’m wrong. But, you know, what the hell. It’s just speculation. And it would be foolish not to speculate.