Think of it as "The Assassin's Creed Effect."
Upon which a well-selling but mixed reception for a game gets a sequel based on the same game engine.
It's just weird for Final Fantasy because we're treading on a new ground (kinda, we do have X-2 and DoC). Direct sequels weren't even a thought for the series a decade ago.
Personally, I prefer this to scraping the whole thing and starting over. It would lead to another long-ass development time, when really its easier just to take the pre-existing engine and fix the problems with the story and level design.
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TheRock ~ Slow dramatic zoom-pan. Doesn't phase the hooded man.