For magic we have creatures that resist (or deflect) fire magics. Or water, wind and earth. I the worst case all of them, which leaves astral doing the job.
For weapons, there is only deflect all, and sometimes you need magical weapons to hit a creature. About that deflecting. I can imagine a creature with a thick skin. Wie a blunt weapon, a hammer, that creature shouldn't feel that much. But if you use a sharp or thrust weapon, dagger or sword, it will go through it's skin, cause it's sharp.
My suggestion is make creature deflect some classes, instead of all.