As a current SAM main which is now more memey after the potent NIN buff I say no just buff the other jobs up to specs. I leveled a NIN after leveling a SAM which felt weird in a bad way because of the weaker dps. Nerfing MNK would create a similar feeling and I would rather not have MNK mains go through that. You would say but current sav content would be too easy if you do that but it has been weeks now and people got more gear and probably get even more geared by 5.1 when these buffs would happen.