*Spoilers* The Past and After the Endwalker MSQ End

[Veloran]

Exactly how effective the echo is with finding specific memories is difficult to say. Ultimately, the problem is that even if you convince them, you still have Hermes sabotage to deal with, and given he isn’t there to help with Zodiark now, it’s unlikely you’ll succeed at forestalling the first final days. It was SE who wrote that limitation.

But that's not what SE wrote. Venat merely suggests keeping Hermes in the dark because he is a "brilliant mind" and could be useful, at no point is he given specific credit for any part of Zodiark's creation or discovering the solution.

But more importantly, Venat still didn't tell them even after Zodiark was created and the Final Days halted. At that point if Hermes had been crucial to their prior success, it had already been achieved and he had outlived his usefulness. At that point there is no excuse not to reveal the truth.