Wild speculation
Looking the epitaph at the end of The Forked Tower from clear videos, and thinking it could contain information about a Holy type magic just like it's FFV counterpart. But it's not FFV's version of Holy, it's FFVII's, a magic that stops threats to the planet. There is a kind of flowing illustration on it which could be related to the flood, and there are 7 spokes on the epitaph. Maybe the planet is actually alive, and the flood was a kind of immune system response. Maybe the people of the 5AA knew the planet was alive in some capacity, and that's where the 'prophecies' came from. Maybe the epitaph is an attempt to document the flood that washed away the 5AA civilizations for the purposes of recreating at will with out needing a world war to wreck havoc on the ambient aether. Which begs the question: what's in the other tower, considering Flare is just a level 50 BLM spell, Ultima?