Nirvana gets -7 perp.
Hverg gets
Myrkr. Admittedly, you'd need 2000 MP (plausible in Abyssea) for a 100TP Myrkr to restore 400 MP, but that weaponskill also lets you stay out of range and restores status effects.
Any run of the mill
ToM staff that a dedicated player can grind out in literally two days gets 5 Affinity or -5 Perp, so this is a one point upgrade to both of those, and they come with spell casting or recast time reduction.
Claustrum currently has no niche. There currently is no single "best damage staff." Making Claustrum the best damage staff and functional in the other roles isn't overpowering it, it's giving it any role at all.