I get the sense that it was nerfed to make Sweet Business more pronounced. In its prime i felt Breakneck was just a better Sweet business. The hidden FF compensated for the smaller mag. But both basically gave you an SAW bullet hose playstyle, Breakneck just didn't take an exotic slot. If i were to balance the two I'd unnerf breakneck, it is a silly hard grind after all. If Sweet is still not a competitive bullet hose choice with the recent buffs add explosive rounds or dragonfly or rampage to it's existing perks.