An interesting writeup of the Willard-Johnson fight. Tl;dr: Willard looked like a scared, passive, awkward mediocrity until the aging Johnson ran out of steam from rushing and punching him. http://www.eugenecarsey.com/boxingnewspapers/news/willard_johnson1915/willard1915sioux.html
I have seen so many small fighters kicking the asses of bigger guys, that in my opinion size only matters when the small fighters puts a lot of weight on him and kills his own speed, stamina, etc...
I feel like those of you who say size is the biggest factor think that a guy who has a weight advantage is impossible to knock out. Whether you weigh 215 or 240 you are going to get knocked out with the same punch. Joe Louis was absolutely BEATING Abe Simon around the ring. Jack Dempsey BEAT Jess Willard for 3 rds. These guys gave the big men of their day BEATINGS. They didn't merely win a decision or score a knockout over a competitive match, they literally BEAT these guys around the ring until either the ref stopped it or they didn't get up. They were completely outclassed and so would the heavies of today.
As far as I can tell, absolutely nobody in this thread has ever said that size is the biggest factor.
So Mrkoolkevin since you know everything about everything what grade did I make in senior year english?