>There are professional climbers who are 'heavy'.
Who? The heaviest I can honestly think of would be Chris Scharma, Magnus Midtbo, Jimmy Webb and maybe Jan Hojer, but all of them would be considered pretty skinny by normal standards. Scharma and Webb are probably around 6' 160-170 lbs, Jan is around 175 I think but he's 6'3", and Magnus is 5'8" and 158 lbs or so but has incredibly strong fingers.
Climbing is a strength to weight sport, so being heavier will almost always be worse than being lighter no matter what. It's why you don't see as many tall professional climbers as you would expect.