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

[BokoToloko]

The events in Meracydia aren't linked to the Dragonsong War. If you have evidence the Ascians were involved in telling Thordan I to slaughter Ratatoskr and devour her eyes or telling Nidhogg to enact 1k years' worth of revenge upon Ishgardians for it, then by all means.

It's not meant to soften the blow, it's meant to clarify. I'll also say again, rejoinings wouldn't have been a thing without the sundering in the first place.

It's pretty hard to prove direct link between Ascians because they make sure to not leave marks in history. Also, the rejoining wouldn't have happened if the Ascians had accepted their world was over or actually tried to do the same, WoL, do, try to improve their lives instead. They're the culprits and the ones responsible for the rejoinings in the same way Venat is responsible for the sundering.

Ah, no. The day was barely won by the WoL who had been groomed for it from the start and given every tool past, present, and future to ensure success, which included the assistance of the unsundered. (Noting that were it not for Emet's sentimentality he would've likely killed the WoL on the spot on the First, so the WoL also had to be a reincarnated Azem for this to play out as well.) Mankind without the WoL and their links to the unsundered absolutely fails to defeat Meteion.

Links Venat had accounted for (she was the one who carried Emet to the aetherial sea). And most of the struggle to fight Meteion would've failed if mankind as a whole hadn't supported WoL in any stage, such as refined adamantite and the Garlean contingent. The entire point of the story is ultimately: Help the world get their shit together and see how your deeds carry over. Everyone contributed. It's absurd to overthink the classic trope of the hero being supported by those he saved.

[Rulakir]

It's pretty hard to prove direct link between Ascians because they make sure to not leave marks in history.

Likewise, you can't attribute all the ills of the world to the Ascians. The sundered all on their own are capable of unimaginable cruelty as we've seen repeatedly starting as early as level 15 in ARR.

Also, the rejoining wouldn't have happened if the Ascians had accepted their world was over or actually tried to do the same, WoL, do, try to improve their lives instead. They're the culprits and the ones responsible for the rejoinings in the same way Venat is responsible for the sundering.

Words are easy. Fact of the matter is telling people who've survived a horrific apocalypse where their loved ones were forced against their will to conjure creatures of nightmare that devoured people in the streets, then had more loved ones volunteer to be trapped in indefinite purgatory within Zodiark just to make it stop, that in their moments of trauma and grief need to move on is incredibly tone deaf. Not to mention that returning to the star was a core and important part of their beliefs and those who'd sacrificed themselves to save the world were now prohibited from doing that.

Frankly, I think the game did a poor job of depicting how terrible the Final Days actually were (not helped by the fact that the return of them amounted to virtually nothing so the sundered never got a true appreciation of what the Ancients went through either). It's more like your loved ones are now POWs, but instead of trying to rescue them you should just forget them and move on with your life. No one would do that, especially when they had a means of bringing them back.

Venat didn't give the Ancients any context as to why they should change (not that it mattered because someone was always going to have to face and defeat Meteion, embracing suffering and despair wasn't going to make any difference in that regard). It was basically:

Ancient1: We have a plan to release those you lost.
Me: Great, do it!
Venat: No, don't!
Me: Why?
Venat: Because...! Reasons.
Me: Uh, that's not good enough, go ahead with the plan.
Venat: *sunder* That's what you get for not doing what I wanted!

Links Venat had accounted for (she was the one who carried Emet to the aetherial sea).

You're just reaffirming what I said.

[Lauront]

Her entire plan relies on Zodiark. In terms of what SHB tells us, it was Azem who left the Convocation out of opposition to summoning Zodiark (reasons unspecified.) The dialogue with the Watcher on the Moon does state that her faction opposed his creation, but I believe it's an error from the writers in the EN version, because the SHB dialogue from Hythlodaeus does not frame it that way (instead, it premises the opposition as stemming to the third stage of sacrifices - sources on the SHB stuff here), it's not repeated in the FR version (here), does not fit with the post-Elpis cutscene and it would make mincemeat of her entire plan (relayed by the Watcher himself just after that) which is to bunker up beneath Zodiark's shield while they identified the true cause of the apocalypse. If the 14 wiki is saying this stems from SHB, it's just wrong. That site tends to be poorly written and injects a lot of headcanon/"spin" into things, so source texts from the game are always preferable.

Venat didn't give the Ancients any context as to why they should change (not that it mattered because someone was always going to have to face and defeat Meteion, embracing suffering and despair wasn't going to make any difference in that regard). It was basically:

Ancient1: We have a plan to release those you lost.
Me: Great, do it!
Venat: No, don't!
Me: Why?
Venat: Because...! Reasons.
Me: Uh, that's not good enough, go ahead with the plan.
Venat: *sunder* That's what you get for not doing what I wanted!

As a further point here, even the Scions are left shocked by what they see in the Plenty in the Dead Ends. This is after they had you relay what you learnt in Elpis and Hydaelyn gave her lines about "suffering" and yet they struggled to believe it. Trying to convince through mere words the survivors of a civilisation that had succeeded in extinguishing many ills that this pursuit could end poorly, without hard proof of what was driving her concerns, was never going to cut it, IMO, made all the worse that the cutscene related to it shows these words being offered at perhaps the worst possible time.