BF3 has had loads of new weapons put in through DLC and no one complained
Yeah and BF3 had genuinly OP weapons in their packs. And actually, loads of BF3'ers complained about the Famas.
FAMAS got nerfed into oblivion, and there weren't any OP DLC guns outside of that. Most of the DLC guns were average and the best ones like the MTAR were top tier but not OP. --- Mike Dawson never returned to the carnival, ever again.
In hardcore it isn't even that OP. All guns are the same and if you test the animation out on mobility you can see that your running animation is slower than if you were holding an MSMC. It actually makes you run as if you were holding an AR.