For an Avengers movie to be a grandiose success, like it was, there has to be some common sense taken into consideration. Why would Hawkeye, a normal guy with no super powers, get more screen time than an Asgardian God of Thunder, a man in suit of armor with enough firepower to level a country, a supersoldier an entire nation adores, and a giant green monster of rage?
It would make absolutely no sense if you see Hawkeye get the same amount of screentime than the Avengers that really matter. And don't get me wrong, I am a fan of Hawkeye (in the movie and comics), but he is just really good with a bow. That's it, end of story. There is very little room for development there, and what Joss Whedon did with him in Avenger is really all you can ask for.