Despite all the size doesn’t matter much talk, size does really matter. It just matters less in street brawls where a single punch can easily take you out. Sustained punishment by trained professionals in a ring setting is a completely different story. Regardless, size gives the advantage of being harder to push around and also making it easy to push around your opponent.
When a person is heavy, it takes less speed for them to build up energy than a lighter person. This means they can punch hard with less effort than a lighter person. When a person is unnaturally large, such as an elephant sized woman, they can generate some decent power if they aren’t too slow.