It never says it in the game, but i could see there be a limit in what Maxwell can create. For example as he creates God, it isn't really God. Since it would create a paradox and destroy the world. It's more likely, he creates his idea of god, which is a white old dude with a white beard. Also god isn't all might in the games and can't do anything specific, other then punch people.
So there has to be a limit to his power. Either there is cap, how powerful his creations can be, or the limit is his imagination. His version of God could only be as powerful as he thinks, a powerful being can be. All Maxwell can think of, is that God can punch really hard, and in context, those punches are nothing special. By comparison Goku can punch people so hard and fast, that you can't see his movement and it creates a loud sound. Maxwell's God doesn't come close to this.
So Maxwell can be beaten easily.