Magic isn't something that's inherited though. Magic was given to humankind by Lavos through the Frozen Flame. They steadily grew to evolve out of using it after Zeal fell.
Same thing, really; evolutionary traits are hereditary. We would agree, I think, that Lavos doesn't "give" magic to every human who can use magic; at best he gave it to a few ancestors and things went from there. Hence, that is why Ayla can't use magic even though she is alive (unlike Robo); she lacks the genes. It would be a curious thing if Lavos gave Crono, Marle, Lucca, and Frog the ability to use magic, yes?
Of course, giving humans magic may not have been an intentional effect of Lavos (and mind, magic is just the assumed result of Lavos, since that is the only clear evolutionary change between Ayla's people and the Enlightened ones). Simple exposure to the anti-annihilation energies of the beastie may have done it as a side effect.
How do you know it was made by the enlightened?
It is a series of floating landforms lashed together by chains, populated by semi-intelligent mystic-like creatures who have mastered the art of taming and riding beasts, it is used as a prison, and its warden appears to be a magical golem-like construct. That is a lot of unnatural things for it to be a naturally occurring anything.
It clearly isn't a construct in the sense that the Ocean Palace is a construct, but it ain't natural and the Earthbounders clearly don't have the power to create something like that. Perhaps it might be prudent to say it is a construct along the lines of a stocked dam lake; humans tend not to create the water itself, we just create the circumstances that allow a lake to form.
Mainly there is no proof that the Mystics were created by the Enlightened, in fact the Soul Sanctum proves against that theory. I don't know if thats what you meant but I still think we should clarify.
Not at all. For one the canonicity of CTDS is debatable (for example, did Crono & Co "really" meet the Dream Devourer? If so, isn't that a temporal paradox since from their POV they hadn't defeated Lavos yet?). For another, assuming that CTDS truly indicative of true Chrono History, if the Mystics are merely a branch of humanity, then it makes sense that they'd still exist in a Reptite/Dragonian dimension. Indeed, it is only if the Mystics are a direct result of Lavos or a specific artificial construct of Zeal that they should
not exist in those dimensions.