One way to save the Ancient world is to teach them how to summon Zodiark without the tempering aspect. So Zodiark would still shield them from Meteion but the ancients would not be tempered into being reliant on him and wanting to sacrifice more life. They can then learn how to deal with their sufferings and convince Venat to not summon Hydaelyn. There's still the question on how to confront Meteion without being able to control Dynamis but surely Azem will figure out a way eventually.
