I don't have the season pass, but I picked it up a few times. I didn't find it op. It was a solid weapon, but I don't see any need for a patch. It's not THAT good. I'm glad the weapons in DLC have been decent, because I found the peacekeeper to be boring in comparison.
I dont think this gun is OP by any measure. Certainly not the case when I used it. However, I do like the gun... just because it is something new and different. Neat idea, and it feels good to use, but I think it is the player, not the gun, that wins or loses gun battles.