FFXV was super unfinished. The final world map is like 15% of the original world map that they unveiled during development. The crazy thing is that a lot of the other 85% of the map exists if you boundary break, it just isn't populated with anything so it's barren terrain. Either way it's clear they had huge plans for the game and weren't able to meet them. The last third / five chapters are practically on-rails like Xenogears Disc 2, rushing you through areas to get to the conclusion. The World of Ruin felt like it should have been a huge part of the game and instead it was like 20 minutes of gameplay.
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Here's the early development world map. Only the lower right quadrant actually got fleshed-out in the game, rest is only seen briefly on train trips and I don't think you even go to Solheim at all. Not having an explorable Tenebrae, Solheim, and Niflheim were such missed opportunities, as was traveling through any of Accordo rather than just warping to Altissia.
For a point of reference, when I was playing through the first 10 chapters in Lucis, I thought that area was like the first quarter or fifth of the game. Turns out that area IS the game, outside of the brief "greatest hits" version of a few other places you get towards the end.