I read the book a couple years ago, for reasons I'm not really clear on. I guess I thought it would be a good read. And it was. It was enlightening, albeit silly and sophomoric. The OP is right that Matt comes off as a cocksure meathead, and proud of it. He's definitely used God as a catchall for all his human flaws.
But in the end, I don't care. It's his fights I pay to see and he's always delivered, whether he wins or loses.
The guy is no hero or villain, just a guy with obvious defects who entertains the shit out of us.