I have posted this before but nobody will discuss it.
This is probably stupid but I think I know why SS didn't get much screen time... He's huge, he is just as big as Megs if not bigger. I have group pic (that I can't seem to post right now) some of you may have seen, it has all the autobots(from the movie), barricade and Starscream, all of them in vehicle mode. Anyway starscream takes up almost as much space as the three bigger autobots all together do.
The only autobot that would even stand a chance against him would be OP and that just wouldn't look right with SS easily being twice the mass of OP. Even OP would have a hell of a time handeling him.
I'm not really going anywhere with this, I just wanted to get the idea out there and see what inteligent people might have to say about it. My point I guess is, how would they justify starscream not just destroying any autobot he went one on one with, when he is 2X their size