I have to disagree with you there. Bruce Lee was benchmarked physically and no one has surpassed him on speed, agility, and strength per pound of weight.
Also, in ufc fighting it's not that realistic. When you put gloves on you disperse the pressure from the knuckle and the more skilled fighter is at a disadvantage. In real life a woman who ways 140lbs could knock out a guy who weighs 240lbs with one blow assuming she was proficient at striking with her knuckles.
It's basically like taking a needle and putting a cap on it, the needle no longer punctures paper the same way - it's just physics.
I don't recommend street fighting though or fighting ever. Freshman year in college a short little guy came up to a d1 line backer in a bar fight and smashed a beer bottle over the dues head, he was 6'8" 350lbs of muscle but the little 125lb amigo nearly took his face off with that bottle.
Fighting is dumb and inevitably results in tragedy outside of a ring/or gym.