This is hysterical. I am a woman and I've literally toyed with men that are 100 pounds more than me in Jiu-Jitsu because they had no experience. Training martials art makes you infinitely more skilled than a regular person. None if it is useless.
I mostly agree with you, and have seen that. A female friend in college was a muy thai competitor. She was tiny, and extremely scary in competition. Very strong for her size, and very precise. She was so tough I wouldn't spar with her, she could wreck me accidentally, because I was very aggressive, and was difficult to predict.
I was a brawler who had some martial arts training back in the day (judo, karate, tai chi, kenpo). I would eat black belts alive, mostly because I was multi-discipline, and they were mostly sport fighters. They could only really fight people fighting their fight or with no skills.
Yeah, a bigger skilled foe will almost always take a smaller skilled foe, but there are exceptions. Extremely skilled or talented fighters break those rules. Some people also are extreme, and crazy people are not predictable, which can give them an edge.
I see, I would love to see how he will deal with a boxer twice his size.

Or just how will he take a punch from the other guy with no gloves and protective gear.
A great boxer will never get touched by a brawler in a straight-up fight, and hit like a motherfucker. Bruce Lee respected boxing more than many martial arts, and studied it.