Thats because its the most dramatic case -but even in your explanation example "Hearns could have been confused mechanically" -thats proving my point. Especially new guys. I use my own experience as my own proof - i was always extremely high fast twitch grow muscle really easy but light noned. Hips are also very fast, and flexible so i can generate alot of power in both punches and kicks. But for some reason, kicks were instinctive but punches were not. I alos spent alot of years power lifting/bodybuilding which reinfored a bad punching mechanic. Ive had the same coach tell me when i first walked in "Man, somma these kids walking in right off the street are better punchers than you!", to " you punch harder than my heavyweight". My coach at the time was a retired Ammy 82-4 boxer , ghetto af and didnt like to give anyone compliments ever. Because id continue to lift heavy, id always fall back into losing my snap for my straights and rotators would hurt my hooks (heavy benching is contraindictacted for smooth boxing)
Ive seen so many guys throughout the years -some guys had what i call frat boy juice power but they'd get smacked around by skinny guys with whip like punches (similar to tommy hearn build) -now was that just finesse? No, they also learn to utilize their genetic frame properly.