size ( either weight or height it both) and strength don't necessarily go together, unless your big person actively trains strength or has strength job, in a ring contest you can make a reasonable assumption that not only is he or she a foot taller, 60 lbs heavier they also train strength to some extent, in the wider world that far from true
they are far more likely to just be bigger but have less strength than you, if you do train and they dont. being big with out the strength to move that weight makes you slow across the ground and to turn, how fight unfolds then us dependent on not letting them use the weight against you, if you end up on the floor pinned by their weight, your in trouble, whilst in motion you have the advantage of both speed and strengh
in myh early 20s I got into a lot of fights with people who were substantially heavier than I, nearly every one was heavier me, I was 150 lbs soaking wet, this seldom seemed to matter much, in fact being tall and supper skinny seemed to be the cause if most if these fights, people making the mistake of thinking they could push me about, particularly if they couldn't see my Bruce lee type figure under my leather jacket,