How can Venat be the previous Azem?

[sidurgu-12]

Azem left because they disagreed with the Zodiark summoning plan in general, but they also didn't join Venat's group either.

And as was explained in ShadowBringers, there was a plan to "cultivate" future life to sacrifice to bring back the Ancients who had sacrificed themselves in the first two rounds of sacrifice to Zodiark.

Here's what Hythlodaeus' shade explained to us in ShadowBringers


Then in Endwalker we also found out that Venat/Hydaelyn also had an additional motivation for the sundering, which was was to also thin the aetheric density of the denizens of Etheirys so they could more readily interact with Dynamis.


You have to remember that the cutscene with Venat/Hydaelyn that plays after the Elpis zone is completed is metaphorical and not a literal representation of the chronological events.
As evidenced by the fact that the Final Days are still ongoing despite Zodiark having already been summoned. It was a condensed depiction of all the major events, not a literal play-by-play.

plus emet and hythol arguing while a man gets eaten.