This should have been an easier, and a lot cheaper, film to make. To start with, location. When you think 1980s, who thinks of the Sunset Strip?
Music in the 1980s was totally dominated by MTV, the best new music advertisement medium every created. But MTV is owned by Viacom, and this movie was made by New Line/WB.
Major problem here. While WB music played a lot on MTV, they were just customers, not part of the scene.
And yes, the casting sucks lizard eggs.
80s hair metal, which is what the movie is built around, came first out of the Sunset Strip. Van Halen, the Crue, Quiet Riot, Ratt, all from the Strip, then all the new acts (yes pushed by MTV) had to imitate that sound.