Let me begin this with the fact that this nerf will DESTROY the guns, sure they will be ok, but these are PINNACLE weapons. Anyways, I would suggest reverting the changes and make Magnificent Howl fundamentally work the same (3 crits), but make a player have to get a precision kill before Mag howl would proc. Once it did proc, then the perk would allow for that 3 crit kill, with the same conditions that it lasts until your next kill or miss. Another idea I had was to keep it a 150, but precision kills would increase its rpm by a set amount each precision kill. I do hope that this can be taken into consideration, and I am trying to be constructive here, and pose new ideas... feel free to post yours in reply.
I'd say make them exotic, or keep NF generally the same and nerf Luna's. Luna's is much easier to get then NF, which is why I think they should leave NF alone.