Maxperson
Morkus from Orkus
I'd just downgrade it to resistance. Despite what WotC is claiming, resistance doesn't really make it so terribly difficult for a non-magical party. Non-magical PCs tend to do high single target damage, so focused fire removes those hit points pretty quickly. I wouldn't plan an encounter with several damage resistant creatures any more than I would plan an encounter of multiple beholders to use against an all caster party.Also, when a creature is immune to nonmagic weapons, the DM can easily ignore that trait, for a setting that lacks magic items.