The timeline of the actual destruction of Ancient society is oddly incoherent. We know that it was destroyed when Hydaelyn sundered Zodiark and the Source, but I cannot for the life of me understand why She is only heard by those who see the Meteor Shower considering She had yet to be summoned by Venat's group.
We are told repeatedly that Zodiark not only ended the threat, but was being fed the souls of "lesser beings" to reconstitute the Ancients who had sacrificed themselves to "Rewrite the Laws of Reality". So the threat was over already and then here comes Hydaelyn, who again has nothing to do with whatever caused the keening, bonking Zodiark over the head and suddenly begins using Meteors to rekindle that spark that unlocks the Echo?
It seems more likely to me that Zodiark may have rewrote the laws but He and His creators didn't know what was actually causing the issue. An issue that Azem went to go investigate themselves. Do you not find that odd? Azem refuses to help either side summon their prospective gods and instead seeks the Source of the cacophony. They felt that Zodiark nor Hydaelyn had the answers to the problem because none of their summoners ever saw the worlds problem firsthand. They only knew the world as others told them it was. They (Azem) knew it had to be something else that was banking on both sides being so inept. It has to be malicious.
It's called The Echo for a reason. We haven't heard Hydaelyn for so long and are now only seeing what may very well be Her Heart (I am inclined to still believe that Minfilia/Ryne are still facsimile creations of Venat/Hydaelyn to help guide their respective societies) attempting communication. Not Hydaelyn the propaganda, but Venat the person. One final desperate plea for help because as we found out in Coil, Gods can be tempered too...