Yeah, I absolutely loved how Stark and Banner got along. Loved their scenes together in the lab like you mentioned. Especially when Loki was talking over the scenes of character to Widow. Just seeing them work together as scientists and getting along was a great moment that I loved. And them going off in the car together in the end.
I'm starting to think if Norton was in this, they wouldn't have had the same kind of dynamic and chemistry RDJ and Ruffalo had. Norton's Banner seemed too serious to match in this context.
Ruffalo had a perfect balance. Likeable, no longer angsty, but more humorous and when it was time to be serious, he brought it. Even the references from TIH it felt as if he had been in TIH instead of Norton. Ruffalo was aces.