Tell me if I got this right: Superman expresses a distinct concept. If anyone used the same concept using differnt language it would be infringmt. So if the concept of "a single omnipotent and omnicient creator of the universe" was expressed through Ahura Mazda and this expression was copyrighted anyone who used th word god to express the same concept would be held accountable for infringment, right?
No. Not at all. Partly because basically every religious scripture (except for very new religions) is in the public domain, so 'Ahura Mazda' would never be subject to copyright, and thus would never be subject to copyright infringement.
Additionally, while the distinctive features of a character, when taken as a whole, can be subject to some level of copyright protection, it really does take a fairly identical character for there to be much chance of infringement. Anyone can write a book about a boy wizard without needing to worry to greatly about infringing the copyrights for the Harry Potter books, but at the same time, the more that boy wizard exhibits traits and gets into situations that resemble Harry Potter, the greater the likelihood that someone could find infringement.
So even assuming Ahura Mazda could possibly be copyrighted, the protection in that copyright would not necessarily extend to all similarly-powerful beings, but would probably only extend to beings with
very similar traits, legends, and so on.
And finally, although the owners of the Superman copyright were famously able to sue the publishers of Captain Marvel in
National Comics Publications v. Fawcett Publications, 191 F.2d 594 (2d Cir. 1951), that case was settled in an era where caped, super-powered superheroes were a fairly new concept, and where it could fairly be said that Captain Marvel would be a non-fair use derivative work based on Superman. Nowadays, it seems like the situation would be different, since caped, superpowered superheroes have proliferated into the thousands, and so it's much more difficult to say that the concept of any one superhero is especially derivative of Superman (or of any other particular superhero), or that the caped, superpowered superhero is an especially-unique concept anymore. The 'idea' of a caped superhero has effectively been divorced from its expression in Superman, since it's fairly impossible (without some very specific similarity) to prove that any one caped superhero was actually copied from Superman. We also live in a world where the ancient Persian gods are just some of millions of other gods, so again, it would be difficult to show that the creator of a new god would have copied Ahura Mazda (he could just as easily be entirely unaware of Ahura Mazda) -- he may simply be appropriating the entirely public domain concept of a 'god' for his own use without actually copying any one god.