I remember hearing rumors that there was originally a lot more focus on the hulk in the early drafts, including more on the widow/hulk relationship and more time being given to show how Banner is becoming more capable of controlling the hulk leading up to a more dramatic and a bigger emotional payoff when he goes on the rampage. I speculated after hearing that rumor that we might have gotten to see some transition to gray hulk.

There is still evidence of this with the "suns getting real low" scenes with Widow, the way Tony talks directly to Banner during the hulk buster fight and uses that line "I know, don't mention puny Banner" as if we should have heard reference to that conversation before, and the hulk calmly just pushing the button to turn off the communication with Widow at the end. It all just makes the hulk/banner feel like a really detached character who never really develops at all throughout the film. Unlike Hawkeye and his pregnant wife/farmhouse scenes the Hulk's character development feels flat without that same level of dialogue driven connector material that shows Bruce actually getting some positive reinforcement and having success with controlling himself as the Hulk before he goes on his rampage.

In my opinion I feel like the film was trying to focus more on the development of the other characters and marvel probably told Joss "no, we need a chunk of that screen time to give information about Thanos and Thor Ragnarok". It feels like the result is that the Hawkeye stuff stayed, but most of the hulk/widow stuff that I was expecting and feels missing must have been cut, probably at least partially because of focus testing groups saying girls don't buy action figures and boys won't buy black widow merchandise.

I also have a theory as well that it probably wasn't always going to be The Vision who handed Thor Mjolnir after using it on Ultron in the big team fight. Notice that when Thor is given the hammer and responds to the person who gave it to him that person says their line off screen. I could see one of the others, say Widow, handing him the hammer instead and the studio demanding that he change it after focus groups determined that it would lead to more of The Vision toys selling. I believe it was probably Widow because she was one of the few who refused to try to pick it up during the party scene and that type of payoff is totally something Joss' would do.