They nerfed most guns so skins and their stat-boosts are almost REQUIRED for solid stats. Shotguns are now worthless.
I haven't examined the new stats for the guns very carefully (I don't play much anymore) but I'm not sure this is true, or rather I suppose more accurately I'm not sure this is exactly a bad thing.
For example, previously the car-4 was godmode gun. You could have literally perfect aim, minimal recoil, and one of the highest (non-lmg) ammo capacity + ammo pickup rates in the game plus still hit the magic 40 damage breakpoint. It was not even a high level gun, I think you unlocked it at level 4 (basically, after 1 mission) There was no reason to ever use anything else, except just for fun. And while car-4 was the worst example, most guns basically fell into one of two catagories: 1. hits perfect stats, good gun 2. does not hit perfect stats, crap gun, never use it ever.
Shotguns were just poorly implemented (and probably still are). I'm not sure how they nerfed them, but the locomotive was a secondary that was honestly better than most primary weapons in the game so I'm not sad if it got nerfed.
Again, I want to stress that I've not looked at the new stats for the guns - maybe they did make everything terrible, I don't know. But they really did need to rebalance weapons, and the only way to do that was to nerf the top tier guns because they were just too good.