I'm 6'5" 240 pounds and in good shape, I wrestled in high school, trained a few years as an adult in grappling here in LA years ago... I've been rag dolled by one or two guys around 190-200lbs (D1 wrestlers) with that wirey gorilla like strength combined with good wrestling skills, it was very disheartening.. Out weighed them by 40 pounds... Very humbling..
Sure weight and size advantages matters but that's not always the case when the skill and farm boy strength advantages come into play for the smaller dude.. Cardio and speed factors also can be hard too to deal with as the bigger guy..