What's the point with that quite lackluster story in Endwalker?

[Iscah]

Same thoughts but with Venat. Why do Hermes and Venat get to be on the finale painting, but Elidibus/Zodiark are nowhere to be seen. Really baffling when you remember they’re the only reason we’re even alive to this day.

Because everyone is in their Ancient forms, not modern Ascian/primal forms?

Including Elidibus requires either a mismatching "not original self" version or his previously unseen form as Themis. Either would be jarring for that moment.

If we had seen him in the course of the MSQ, he would almost certainly be there. But in the existing layout of the narrative, it is difficult.