You underestimate the potential levels of delusion possible. Brooks never did sports, never had to adjust his abilities on reality before and got fed a gigantic ego in fake wrestling. His post fight speech vs. Gall and behaviour afterwards really showed that. He coped not by adressing that he lost but by playing up annother character. The elderly experienced martial arts star.
As a martial artist who competes, his delusional mind always was his biggest weakness. Not his body or skill that would have evolved more with the right attitude. No one is that spastic / uncoordinated after years of training otherwise.
Hi lived and imo still lives in a complete bubble. And "backing out" was not an option because he got paid a LOT of money to enter the cage. So thats really not something were he gets respect.