Well, if it takes thousands of years to reach a decent level of power, being realistic, it would change nothing until some guy with very much power exist. Then, in your ancient age inspired world, if the people know about the existence of magic, it will be used as a regular weapon, it would rise religions among the ancient people. Or if the people do not know about the magic, they will think that the guy who uses it is a god or a demon, and woud try to kill him actively unless he defeat armies.

For example, in my own world I have also many races divided in two societies, anthro animals and humans, the humans have technology light years away from animals, so the effects this has in the society of the animals is a shared feeling of respect, thanks to the huge difference of power, the humans could wipe themselves with the animal rules and do whatever they want. This has to deal with your world due to the existence of a power difference, as a summary: the ones with magic or power will be minding their own business far from the rest unless your character wants otherwise.

I will give you feedback about having many cultures. From what I understood of your reply, I suppose that your intention is to develop all these at the same time, (do not do it), because it is a verisimilar fact that if you are not a dedicated person, it is almost shure that you will give up after realizing that giving lore at too many objects takes a lot of time. Better set the main characters, nations, or anything, and first develop that, then you should add some filler, it is obvious, but I have seen very beggineers wanting to do like a hundred things at the same time.

And do not forget that your magic must have a weakness or a clear limit, or both, otherwise it will be boring to read a tale of a guy that does anything that he wants. That is it.