Elidibus is definitely shafted in terms of screentime, which is a shame because he likely could have balanced the discussion to not be so skewed in Hydaelyn's favor, and bring back some of the nuance Shadowbringers built up, if he'd only had more scenes. That being said, I honestly really like the way his final fight was handled in 5.3, even though it is very much FF1 fanservice. I think what Berteaux was suggesting earlier was that while not Zodiark in form, Elidibus in that moment embodies what Zodiark was always meant to be, a savior made to bring about the world's salvation. The actual Zodiark you fight is a sundered husk of his former self, being piloted by a raving madman. Elidibus was the one selected to control Zodiark and stop the Final Days, he is his true heart, so in many ways he truly is as he proclaims: 'Mankind's first hero' and the true Zodiark.

And if I may also be a bit self-indulgent, I like to think with Endwalker in mind, that some of the lyrics in his theme 'To the Edge' allude to the Convocation acting without the knowledge that Venat could have provided to them, and how even he might have felt deep inside that Zodiark was a temporary solution to a much larger problem, that couldn't be seen:

"Without a compass, wandering, lost in lies of faith.
(Faith slowly wasting away)
Only alive in fighting death's amber embrace.
(Our hearts beat, loud, unafraid)
On hands and knees we pray to Gods we've never seen."

It's really interesting, it seems to me like part of him believed that there was something deeper going on, and the way the lyrics go, it makes it seem like he knew they were stumbling around blind to something important.