Well, I used Gauss a lot, mastered it, ill tell you where you are wrong, not wrong but the good way to play with it. First i played it with sniper scope. First gun that i made my high score 33-3. 30 kills without dying, almost all were headshots, more ammo than DSG, if someone is just a tiny little bit injured you can kill him with 1 hit.
But the next thing that it was very useful was using the Gauss with red dot sight or assault scope (personal thing), Nova as a sidearm, for the modules i used Energy Transfer, cuz its good for the hit and run tactic, Blind Spot, cuz why not, and the most important thing, Weapon Pro. Just get a body shot and switch to the sidearm, secured kill, and they cant run away cuz you took all of his energy. So its not quite useless, you just need to find the right tactic what to do with it. And if you are really accurate, giving headshots it can be better than DSG just cuz it has more ammo.