The barrier protected the sundered but it didn’t protect the ancients, if venat didn’t sunder the ancients then the final final days would have continued unimpeded while they tried to come up with a solution to a problem they didn’t understand or couldn’t properly interact with (since ancients can’t interact with dynamis properly)

So it basically amounted to a split second decision
1) risk it and hope someone fixes the problem before the final days consumes everything and removes any future chance of them fixing the problem
2) sunder the world to buy time to fix the problem

I 100% agree that venat is in the wrong for not attempting to do anything with the convocation to alert them of Meteion but we also don’t know how much time passes between elpis and amurout, the EN version of Elpis strongly implies it’s not a lot at all, plus with Hermes being Hermes how much can venat really trust the convocation beyond Azem, how does she know that the rest of the convocation minus emet selch doesn’t support Hermes plans