SG is by no means bad, it just exchanges clip for a high accuracy, good damage, good firerate, nearly non existent recoil and really fast reload speed. A decent SG needs 5 body shot to kill someone, so in theory, if you hit every single one of your shots, you can kill about 4-5 players in a single clip. If you want a gun that has more clip just use a galil or something. There's no reason to make every single weapons the same.
Edit: I meant 5 not 4
Edit: I meant 5 not 4