Originally Posted by
Verterdegete
First of all, strength is very important in melee combat. You need strength to block, to parry, to push your opponent away, and of course - to deal the blow. You have to be able to keep your composure, and break the other guys composure. As the weight difference increases, the lighter guy is in bigger trouble.
Secondly, heavier guys are taller in general. And with height advantage also comes the reach advantage. The guy with the longer reach has a much wider kill field, while the smaller guy has the additional problem of having to close the distance. Reach difference between a 60 kg guy and a 120 kg guy (this is Baikalsan's genius example) is 0,3 meters. In a fight, this is huge.
Now, you can say that the smaller guy can duck, dodge roll, run around etc. But that comes with a price. Those moves are very expensive energy wise. The smaller fighter will gas out much much faster that way. It's much much more energy efficient to block and parry. Using a longer weapon also doesn't help. The bigger the weapon is, it gets more heavier and more difficult to use in an agile way. And btw, the bigger guy can also use a longer weapon and extend that reach advantage even longer.
The problem here is that people think of a 220+ pound fighter as a stereotypical strongman that usually gets cast in movies to play the big guy. A guy like Mountain in GoT. A clumsy flesh golem that just swings around and crashes stuff. While in reality, 110+ kg fighters look like this: