None of them are meant to be the most powerful, they are all sidegrades to a core concept. The bonus to the Super Shotty is in its mobility, having arguably the best out of the base loadout weapons.
Also it’s called the Super Shotty in reference to DOOM
Melees don’t need a damage boost, they need proper hit detection, which is an issue that the devs seem aware of. They will effectively do much more damage when they work properly.