-Better at close ranges
I think that's the fear the devs have, it ending up dominant without there really being a drawback that isn't too steep, like once you start to mess with damage-numbers etc.
I posted this somewhere else, too, but I think semi-auto shotguns would be broken. Not because they would be too strong, but because everything else is garbage.
That being said, NWI decided to add in an MP7 that uses 5.56 and has no recoil (also called the VHS-2) so I guess they don't give a fuck about balance anymore, anyway.