OK, Gohan is a SSJ2 in that movie (what is contradictory, because he NEVER master that transformation, and never transformed so fast, he needed time to transform even being angry (and he doesn't appear angry, just serious)), but is the weakest of all SSJ2.
We don't know how much, but Super Perfect Cell was able to down Teen Gohan (a lot more powerful) to half his power with a "weak" ki blast (i say it because it was destined to Vegeta who was KOed, he didn't needed much power in that attack). Broly didn't did that.
But that movie is a bit the Super Perfect Cell recreation (the end is almost the same: in Cell Gohan and Goku (spiritually) defeated Cell because Vegeta distracted him; in Broly, Gohan, Goten and Goku (spiritually, he wasn't there really, like in Cell's case) defeated him because Trunks distracted him.
Is not really original. That movie has lots of mistakes: Gohan SSJ2 wasn't able to beat Broly but Gohan SSJ and Goten SSJ could, Broly SSJ couldn't kill Videl in a punch, and Videl was able to dodge one of his attacks.
In the deppest of my heart I believe Gohan wasn't SSJ2, but... if Toei said... Toei have no idea about DragonBall...