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

[Lauront]

So I'm curious about this. I understand the information comes from a QnA, but the implication that if one piece of the soul is lost then all the others are too. We know that death doesn't qualify for this as Ardbert died without us dying. The soul being destroyed begs the question, do any of the souls in those primals go back to the lifestream? We summon Hyth so that seems possible, but it also seems contradictory. Also, if one soul shard being lost deletes the rest, what about all the blasphemies? Obviously there are now several shards that are just lost but did that delete their reflections too?

That information is specific to primals, I believe. Reproduced:

Q: Were Zodiark and Hydaelyn completely destroyed? Or there are still Sundered parts of them on other Reflections?
A: To be really frank on this one and to give you a very straight answer here, Hydaelyn was completely destroyed. Similarly, Fandaniel crushed Zodiark’s heart which is his core and that completely destroys Zodiark. There were of course parts of Zodiark in the other Reflections when he was sealed and split across all of them but at the same time of his main body was destroyed, they all would have also faded into oblivion.

For some reason the souls must've been housed with the core, on the Source.

I suspect she probably did what you suggested and somehow retrieved her other parts.

I have a theory that the story we got is not the story that was originally written and some pieces were left behind in a rushed rewrite.

Based on this, I am inclined to agree. She had also expressed concerns about this before, here.

Things like that line about Hydaelyn sundering herself doesn't make sense within the story we were shown. If she was sundered, why did she become weaker against Zodiark with each rejoining? They'd be gaining strength at the same rate.

I'll see if I can dig up anything on them addressing this. It would be compatible with an explanation like Xirean mentioned, whereby she gathers her shards up, so she's back at her full strength early on, but as the Rejoinings proceeds, Zodiark gains more and more power.

Other scenes like in Elpis when we're shown how to use the echo to read the history of a place also seems out of place and causes story inconsistency.
That means Venat could have easily shown trusted people the truth of what they were to face. Why would Emet & Hytho not even bother taking a peek to see what happened during their mind-wipe and that Venat & Azem's familiar also entered but didn't come out? Really?! No one was the least bit curious?

If that scene weren't added, those questions wouldn't come up... but it was. So what does that scene really add to the story we got?

Agreed.