Good post. Underestimation and intimidation are almost never simultaneous by definition but either are advantages. Extra pressure to win can be a motivating factor but I believe that the pressure greatly outweighs the motivation. Everyone who fights doesn't want to get beaten up and wants to win for a number of reasons but greatly increasing the pressure will tend to inhibit performance. And there's a flip side to motivation: you get less credit for beating a fat man than a man in shape. And while it's not absolutely certain that someone will take losing to a blubbery guy much harder than to a chiselled guy, it's overwhelmingly likely. The aesthetics of it for one look terrible and it's going to cost you more respect and hit you harder financially. You are going to be trolled more for it. This is a big part of why AJ's defeat to Ruiz was the most humiliating defeat of all time and had him breaking down in tears in his apartment eating ice cream for three days. As for narcissism, someone excessively worried about how they look is less worried than they should be about fighting. And narcissistic bodybuilders (or anyone really) don't take well to being humiliated by fat blobs like Ruiz. I don't think more sweat is a silly argument. It's marginal sure but it's harder to grip a very sweaty body, hence the fat athlete has another advantage in the clinch. Muscle is much harder to put on than fat and there's a far harder limit, so an athlete who spends a huge amount of time and energy lifting weights (also exposing himself to more injuries) does not have so much time, energy or health for boxing. The training regimen of a muscle-bound athlete is also more likely to be miserable and lead to burnout. I'm not talking about stripping your body of muscle and replacing it with fat: muscle clearly has many of its own advantages that are absolutely necessary for an athlete. But if you can put on 10-20 pounds of fat without compromising your speed, stamina or agility, why would you not do so as a heavyweight? It's virtually a pure advantage.