I've never played Final Fantasy. But to use an example of an alternate reality I tend to take no issue with, look at Fullmetal Alchemist. I'm no expert on it, but from what I've seen, humanity is basically about 30 years behind "our" world in a lot of areas because of the focus of many minds on Alchemy. Although, I'll admit, their having automail when that kind of tech would take incredible understanding of the nervous system kind of makes me twitch when I think about it.
But part of the point is, I don't have to think about it because I'm not the writer. I can't help but get sort of lost in the history of a world or culture, because I feel the need to understand it for my own sake.
For the record, I'm sorry if you said this before. My memory isn't perfect, so maybe you said it and I put it out of my mind, or I didn't understand it in the same way you did.
Here's the problem I have with the war wiping out all technology and putting them in an apocalyptic past. If that had happened, then the magicals would have won (when they clearly didn't). Because if we place the war in 1500s tech, or even 1700-1800s tech, humanity didn't really have anything that could compete with the kind of destruction you are talking about. If we say "oh, it was 500 years ago, technology was roughly where it is now, or maybe farther, then everything was destroyed and we forgot it all" that presents it own problems because it's hard for me to believe that everything could be forgotten. I'm assuming the magicals were too spread out to warrant the use of a nuclear bomb, so that option is out. But we would need wartime tech to be roughly on par with at least 1940s to have a chance against magic that could do that. Even if the humans had their own "magic-infused technology" the whole time.
If all of this happened before the computer, then I was thinking that the early control methods were based on magic-infused tech and perhaps early experiments with electricity.
I... can live without knowing that for now. But I need to know at some point because it's a part of Joseph's life.