Peacekeeper and wingman are gg early game. They are flat out too strong and low skill cap, both of these weapons can completely kill a fully armored squad(literally all 3 of a squad) without reloading, without any attachments on, minus skullpiercer for wingman. Peacekeeper should require a perfect chest-hit with 1-2 pellets hitting the head to get 100, or more, damage. Wingman is spammable and one of it's main benifits is it's ammo efficiency. Reduce wingman rof and I think you will find it more fair in comparison with other weapons.
I've seen the rate of fire decrease on other suggestions, and I am inclined to agree, I still think some of my suggestions would work as well, perhaps coupled with the rof adjustment, but I am not sure if doing all of them would be fair to the gun, after all it still should be viable. As for the peacekeeper, I can't disagree here, I watched one of the Twitch streams I watch have a guy in his squad, rack up 13 kills in one run, without even stopping to catch his breath, and with no assistance from his teammates using it.
He literally ran through the map, charged every enemy squad they came across, and downed all 3 of them in 4 to 5 shots. Only reloading maybe once in the fights. That's personally rather ridiculous, but I am not sure how much of a damage drop it really needs, after all we still want it to be a strong capable weapon, but there just ins't any limitation on it other then it's slow fire rate, and small ammo capacity. I am not even sure how helpful my energy ammo suggestion would be, at least with it like that not every player by the end of the game has one, and those that do will be limited on their ammo supply.
