There is a growing need for bodily diversity in superhero comics and that can be a good thing. That doesn’t mean there should be more fat characters but it’s also dependent on the character’s conditioning and ability. If Nightwing’s a gymnast, he should look like one considering that’s what he does but he’ll be shorter than he often is portrayed.
This can also be applied to Catwoman when you think about it. Batman shouldn’t resemble Superman in build and face. There should be room for fit fat and thin people too though if they ever existed at all, they’d be a minority. Keep in mind that some of the actors that get to play these characters don’t fit their intended body types either.
Somebody who’s naturally thin like Hugh Jackman would have to work much harder and even go on a diet to fit the roles they’re in. If he were a natural mesomorph, this would come easily for him. But with actors, they’re sometimes so arbitrary that they’re bound to disappoint fans.
It wouldn’t be any better if actors were to strictly adhere to the body types given to characters but would be good to have more superheroes engineered to have their own body types and faces.