I was kinda thinking
gears dont use magic normally (unless stated otherwise)
physical attacks dont use magic

so he would only be immune to magic spells, meaning from my own group
Zeke and Meona, all the others use gears, plus it is also a downside, cause healing magic will also have no effect, so if runa would to heal him if he is too wounded for regeneration, she needs to mix her gear and magic to heal and that wont work
hecate, ophelia, runa when normal, yumi all can beat him with the right teamwork or smart use of their gears.
Stella can beat him with rook and dragon strength but her fire breathing is worthless.

when you think like that, would he still be OP?
if so I would easily lower it to resitance