
Originally Posted by
Cleretic
Venat had a very good and immediately understandable reason not to tell the Convocation, despite that being what she'd do in any other situation by her own admission: because she knows what their standard procedure is going to be to finding out this unknown, and that it's not going to help. (We also know this, because Emet does exactly their 'standard procedure' with Hermes and Meteion and only makes things worse.)
On the other hand, you might remember that there's a certain pretty big step between 'Zodiark dying' and 'coming back from the moon'! A step that proved that, while there's hardly a 'highest authority' on the Source, there is one that's a few steps ahead of the Scions on this particular subject, for which this whole subject is very much a known situation, and should probably be the first point of contact on getting back down there. Said authority is hardly an inherently trustworthy power, and proved that extremely clearly just a bit earlier in Endwalker, but given the scenario put in front of the Scions, were a clear first point of call.
Far from being parallel situations that should or could be handled in parallel ways, these are actually exact mirrors that require opposite approaches: Venat was faced with a situation that gave her clear evidence on who she couldn't contact, while the Scions were faced with a situation that gave them only one option as to who to contact. I don't find seeing the differences here especially complicated, and I'm sure you don't, either.