Yay! You figured it out!
There was zero evidence that Zodiark wasn't permanent. Had he not been killed him, he probably would have lasted forever. Not to mention, Venat's group didn't have the proper information either as she didn't tell them anything important. Is the convocation supposed to believe any random group of people that opposes their decisions, especially when the people in question don't know crap either? Venat didn't tell her group nor the convocation about Meteion. Maybe if she did, her group would sound less like a group of raving lunatics.
Then work on making a different one. The Ancients would have a MINIMUM of 12k years to perfect their new model. You can't seriously think they're so stupid that they can't accomplish that as a major project over the course of 12k years. This is the same civilization that created Zodiark. As for Hermes, there are few people researching it, not one. Lock him up or kill him. He's an active threat to the star.
Need creates innovation. The Ancients are used to doing everything with aether, but if they are informed that they need to use dynamis, they'll innovate. If it turns into a monster, that's what kill switches and experiments are for.
Who said the ancients would only get one chance? The only reason we only had one was because Zodiark died. We were on a ticking clock to solve the problem. Again, the ancients have at LEAST 12k years.
The only piece of evidence that says they couldn't is a line from Emet saying they can't. The rest of the story seems to say otherwise.
Venat didn't give tell them about Meteion. And no, checking in on the thread isn't stalking, and I'm also replying to multiple people here. Calm down your ego Oatmeal.