Agree, I think the excess weight makes him poorly balanced, leading to poor coordination, meaning he struggles to actually use his strength. By the time he has his body moving and under control the guy he is battling with already has the physical momentum. It leads to him looking flat footed, and slow to react.
I look back at Rio and Vidic, those guys were very effective and powerful in one on ones but were so lean, Vidic especially in the flesh was much smaller than most people expected him to be.