Details absolutely are important, but I think your last paragraph sums up my thoughts: Isayama isn't a Brandon Sanderson. The setting is obviously important to some extent, but I don't think it's something crucial to the underlying story.
I like detailed worldbuilding. Again, Sanderfan!... but I don't think that Isayama's jam. He's interested in telling a story, and he gives us enough information about the setting to facilitate that... but I don't think he's planned out the world of Titania much beyond that.
And I don't mean that as a criticism! He's just a different kind of storyteller. It just makes me surprised/confused as to why people pore over his maps so much; I don't think knowing if this story is set on a past/future version of earth will really tells us that much about the conspiracy, setting and so on.
... but that's probably my own biases at work!
(Also, thanks for the above post, was interesting!)