I forgot to add this to my previous post, and honestly it would have made things easier. Magic has two definitions according to Fairy Tail. 1: Magic is the physical embodiment of the spirit. If we take this in to context spirit can be defined as both a type of consciousness/sentience and animating force, which implies sentience. 2: Magic is a source of power. Once again, power is a type of energy, and with a basic grasp of chemistry one would know that energy is not consistent of matter, and is thus not an object.
Arc of Embodiment is interesting in that you are correct, it could create a Zeref doppelganger, but even then it wouldn't have the knowledge or experience of Zeref, which would probably leave it unable to use Black Arts. Also, though it may seem at first that it could have the possibility to use Black Arts, it would be much more likely that it couldn't since the user would have to have prior knowledge to do so. I agree that it does have the possibility to be abused, but that in its own does not make it OP.
I'm not going to lie. I believe Chuckles may have used the wrong wording when addressing the use of Black Arts, but as I said before, the lack of knowledge mixed with the nature of Black Arts seems to be the primary reason for their exclusion. Only three Black Arts (Demon's Eye, Living, and Death) are known and of them only two (Living and Death) have had their abilities described effectively. That's not to say that Demon's Eye should be banned either, seeing how it's been allowed so far.