What lore do you ignore?

[sidurgu-12]

Wording on that is odd. Azem did not join Venat. So who did they defect to? Had Azem just abandoned the Convocation for their own cause they would call them a deserter.

Was there a secret third party in the Zodiark vs Hydaelyn debacle that Azem joined?

I think they kept it vague on purpose. For me azem kept doing what he did best until he got hit by the sundering.