There are a number of great movies in which rock, and other musical genres, play an integral part in the larger social messages they are attempting to convey, and here's a list of some essential ones that do that better than most.
Whether your screenplay is written in three or five acts, an audience can only truly appreciate a complete story, so I say why not implement a proven form that has satisfied audiences for over two thousand years.
'Forrest Gump' arrived 25 years ago and became a phenomenon almost immediately, but, as with most mainstream hits of the past, not everyone loved it, and there has been a very vocal anti-Gump contingent essentially all along.