Quote Originally Posted by Vyrerus View Post
No, the impetus for Hydaelyn's creation was specifically their fear of Zodiark's power going unchecked. It's pretty clear that fear was the motivator, because summoning a god that would need to be maintained in much the same way as the one it holds in check is clearly not a real solution, but it was the one they could think to muster that would work, at the time.
No, the impetus for Hydaelyn's creation was that summoning Zodiark doesn't actually stop the Final Days, it just delays it. So they need to summon Hydaelyn to create a permanent solution. You hear this from the recording of the Ancients that summon Hydaelyn at the end of Anamnesis Anyder.

What's not directly clear here is what is Zodiark doing that just causes The Sound and the Final Days to come back around after an extended period of time.