These are some good points. I have a theory on how all of this could hypothetically be correct even if the City is somewhere else. Since the City is all that’s left of Humanity, I think it would be logical to assume that the original residents came from multiple former cultures. As you say, native villages may have survived the collapse more so than others and brought their old way of life with them. This could explain why the culture of the City may be mainly based off of older native cultures I don’t have any big theories on where exactly it is but I remember seeing the City from the Farm, which was in the [u]European[/u] Dead Zone so I think it must be somewhere around or in Europe.
Another option is that The Last City is still considered the home to the last of humanity with native communities still existing elsewhere because it wouldn't be the first time we were overlooked on a census lol