Just because it’s hard to kill him doesn’t mean he’s actually doing anything
In fact, the harder he is to kill, the more damage that means he’s taking since Roadhog can’t stop the damage. More damage taken means more ultimates thrown your way, and that’s a pretty big liability.
The Roadhog needs to actually do stuff to offset that, so it’s a question of if the other things Roadhog does are overpowered or not.