I know it has always heated up quick, spun slow, and had dubious accuracy. None of that is what makes it awful though, nor is it the damage. It's always been the push. The constant, endless, impossible to escape push.
On my No Res video you can see our Shae get pushed off the bridge at one point despite trying to duck behind cover, being shot from a considerable distance. This weapon made a lot of people aware that Lycus' shield doesn't block push effects, he can be completely stunlocked through his shield by this gun, until he's either in a corner or off a ledge, despite taking 0 damage.
The nerfs need to target the problem area, and damage and heat were never the main problem. The video where I antagged with it above shows how dominating it is to anyone on the receiving end, when I killed 3 Raiders within 10 meters of me ALL while I was wounded. They all charged me to land a finisher and I just pushed them away until they died, including a shielded Lycus. The push is so fast and consistent that you can't even raise your gun to shoot back. It pushes anyone in any maneuver, be it jump, roll, whatever. I have wounded Kons as Alicia before and jumped literally in his face to finish him, and I always get pushed away to death because the first bullet pushes and I get re-pushed every half a second.
I've been on both sides of the gun enough to know that the push is ridiculous. I think the damage has dropped too much and is affecting pve, but push has only been strengthened with the last patch, pushing 7 meters instead of 5.