Most fatties in the OW universe are not running, battling, shooting, saving the world. If they were, they’d lose that weight within a few months and pack on some muscle…
Roadhog aside, because he has a hook he can be lazy and not run as much. Plus I wonder if his Breather has lots of calories.
Can we not make heroes in games fat or ugly? (Horizon 2 & Fable I’m looking at you) Most of us play games to escape reality not represent it. If I play a male hero in a game I want that guy as chiseled and hot and beefy as possible. Because I want to pretend I’m that guy. Or I want to play the hot curvy woman because in RPG’s they often have the most aesthetically pleasing outfits 
And come on… have you seen the other blizzard games? Warcraft anybody? Those proportions are the furthest from realistic and that’s why they’re amazing 
Warcraft females are okay too I suppose 