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

[Xirean]

I played the game where it's casually hinted at multiple times that we were Azem.

You mean where multiple characters noted the similarity of the WoL's soul to the soul of Azem.
Hythlodaus: "A bit thin in the aether, but it's soul is almost identical to Azem's"
The WoL introduces themself as "Azem's familiar" to several people.

It's not possible the WoL existed in Elpis-- they're a sundered being.

What do you think Elidibus did with the crystal tower? Send the WoL into a fever dream or a simulation? It was time travel which the tower is able to do because of Cid, explained in the sidequests for the dungeon The Twinning. It's the entire reason Shadowbringers was able to happen. It brought the tower to the first along with G'raha Tia.

Also Elidibus just conveniently remembers us despite never having his memory affected by Kairos...?

When was Elidibus effected by Kairos? He's not part of the Elpis MSQ where that device is relevant.

So by extension, there's an original past time line that exists independent of our visit.

How I wish that were the case.

I'd be interested to know how the unsundered Ascians—Lahabrea, Elidibus, and Emet-Selch—avoided being kicked into 14 pieces by Hydaelyn.
A4. https://youtu.be/WRpdIL7_NII?t=13301
Summary: Venat intentionally left a tiny flaw in her sundering attack, a "crack" for Emet-Selch to wiggle through. This was a gamble because she didn't have full control over the sundering attack, she could not be sure Emet-Selch would live.

How is it a gamble and how does she not have control if she knew she was going to it and the result because we told her? Riddle me this

A few things on this. The question is in regards specifically to how the trio escaped the sundering and not if Venat knew if the sundering attack would shatter the world or not. The "gamble" on Venat's part was if she could successfully keep those 3 unsundered or not, which she was able to do as we see in game with those 3 still being unsundered. Ironically you have actually provided evidence that goes against your claim and is one of the bigger pieces of evidence that people have used in this thread to prove that Venat did the sundering on purpose.

I ask you again. What game did you play?