He didn't beat Mike for the championship
George has said extensively he's afraid of Mike, no so much physically or based on skill, which he was intimidating, but Mike had a way of getting into fighters heads. If George could overcome the mental part, he could not only take the physical beating, but he could fight better and beat Tyson.
It's one thing that be mentally not intimidated or scared and just survive or get knocked out, but George would beat Tyson.
George wouldnt be a big dummy for Tyson. Tyson would effectively chip away at him, but Foremans in ring experience would lead him to make continual necessary ring adjustments, and not to discredit Tyson, but he wouldnt have rebuttals for all of foremans adjustments. I wont say Tyson would get frustrated, but because Tyson would have to effectively change his approach since Foreman is able to adjust and eat his body shots, and block and parry his hooks, Tyson is going to have to adjust on the fly and Foreman has the ring acumen to get him during that time. Whether he catches him with something big or just takes advantage of striking while Tyson is trying to find something different that is effective.