To be fair that blast in the movie didn't hurt anyone besides unicron, even all the autobots that were INSIDE of him. So I think we can assume it was directed just at unicron.
I agree though, the autobots in the movie were doing SOME damage to unicron and in the movie they weren't even close to planet busting. So surfer should beat him easily.
In comics I thought unicron is pretty much like galactus so he'd win. but someone who actually read the comics should say something instead of me.