Honestly heres what I think the guns need for balance. This is pretty general so it can be applied to everything.
First I want the damage dropoff to be far less steep, and be more of a curve. At the ranges in this game that are typically fought there shouldnt even be damage dropoff but as It seems necessary for balance, im okay with it. I just want it to be less: at 15 feet im doing 50 damage per shot. At 16 feet im doing 5 damage per shot. Because thats honestly how it feels.
Scopes. Different guns need to have different scopes. Snipers need to simply not have access to cqb sights or ironsights. They should be scopes only. On the flip side smgs should only have cqb sights.
Extended mags and mag size in general needs to be looked at. Secondary smgs should not have access to the extended mags at all. But since the curve is better, they wont be so useless without it.
Less bullets means players need to be more accurate. Damage can be upscaled to counter this to some extent but these sorts of changes would likely bring weapons together. How much? Im not sure. I can look at the big picture but with little details like this, well im not here to do the math. Just to suggest ways to tweak the weapons sandbox.