Really wish I could remember the fighters name, but there was a story a few years back about a Heavyweight sized guy smacking his girl in a bar, and one of the UFC Lightweights (back when that was the smallest division) dragged him outside and ended up giving him a fairly serious beating.... Was from the earlier years of the sport.... and while I can't remember the name I do at least recall being surprised because the fighter in question wasn't more than a mid ranked guy.
I think most of the posters are vastly overestimating the value of pure size, when compared to elite level athleticism, experience, and training..... I don't really care if MM is a manlet, dude would almost assuredly positively demolish anyone who isn't in shape, or doesn't know what the hell they're doing..... And hell, in MM's specific case, even if a bigger guy knew how to fight, I'm not sure MM would ever be in any real danger, so long as he had room to move around... his cardio alone would be a nearly insurmountable advantage vs most people.