I've thought about this about a lot of the games. Like where you have an optional boss who is more powerful than the actual boss. Why can't they just save the world?
I have to do everything around here!
The game would be a bore otherwise. Though the villian using the ultimate weapon to destroy the world, that makes sense.
Screw the transforming into a god thing, just let the ultimate weapon take the heroes out, while they're still lv 50-60.