Ill give you that - they built the Hulk up throughout the whole movie, he did steal the show, which I didnt agree with. Could have been something to do with them not having a proper introductory "Hulk" movie leading up to the Avengers like they did with Iron Man and Thor.
Your going to always have some " Maverick" loose cannon on a comicbook team.
For Avengers it's Hulk (black Panther is the brooding anti-social one), the X-men, it's Wolverine/Logan.
The Justice League, it's Batman. With Wildcats, I believe it was Maverick (not sure). I'm guessing when they decide to put these characters on Teams, their individualness is stressed, their "anti-hero" and "Eff the Man" mentality is their strong points, so when the movies come along, they put more stress on that, as it gets more people in their seats.