Completely different sports of course, but at my peak as a flanker I was very mobile and agile at 80kg while only being 5'9". Not overly bulky either, I had a low bf% and visible abs while at that weight. Still "lean" as Dules would probably put it.
I'm currently 75kg, and find it hard to believe that elite sportsmen in the CB position are my weight.
Weight would probably make a big difference in the air, and also while playing against target men who play with their back to goal. Kos' weight obviously isn't a huge detriment to his game, I'm just surprised that's all.
