Does size matter in a fight? Does a bigger guy have an advantage, or does it really come down to speed and technique?
The short answer is yes, Both height and weight play significant roles when determining an advantage in a fight. the heavier are usually stronger, hit harder and easily can outmuscle opponents if they get their hands on them.
Small fighters have less mass to set into motion, so they can move faster and use less energy doing it, in some cases having extra size MAY not help you if the opponent got the tools and the talent, even great size difference can be overcome, technique is a bigger variant.
In the video below, you will see the reason that combat sports separate fighters based on weight class, unfortunately this smaller guy learned that the hard way.