Post-Shadowbringers Speculation

[Kallera]

If J may add to your theory on how Sephirot and Lahabrea may be linked...

Sephirot is regarded by its worshippers and used by the allagans as a god that creates life.
Lahabrea is known in Amaurot as a, if not the, top authority on Creation Magic, and said to be skilled in phantom creation. As an Ascian, he was behind a lot of the “get disaffected locals to summon primal, hilarity ensues.” plots up until his death, which was a (bastardized?) form of his practice.