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

[RukoBoshi]

The moon was quite a disappointment. It was mostly just to just waste more time with the lopporits, when they could have at least had it dealing with Zodiark and the final days of the Ascians. Instead they did what I consider possibly the most egregious fault of EW, they just killed off Zodiark unceremoniously. Zodiark, the big bad they had spent nearly a decade building towards, the big bad they added intrigue to in ShB, and we don't ever meet Zodiark. Zodiark is not a character, it's a simple plot device that gets possessed by Fandaniel for us to have a boss fight so they can sweep him away for the "real big bad all along".

And for the record I'm not salty about Zodiark not being the big bad guy. I'm salty we got NOTHING of substance with Zodiark after all this time and don't even get to meet the real Zodiark. It is such wasted potential all to just be a subversion.

Considering we killed "Zodiark" back in 5.3 i don't understand your confusion.
Wasn't it established that zodiark didn't have an actual personality aside from Elidibus back in Shadowbringers ?

At best it would have been Zenos instead of Fandaniel in their, but he was never going to be his own person now that his heart is gone.
It would be like having the primal king Thordan without the Archbishop at the helm, just an empty husk.