That's just not how development works. The very specific details regarding all of this are hammered out later in the cycle. The project planning stages aren't as significantly defined and story usually takes a lower rung of development for Blizzard, particularly in regards to the patch content, which is what we're discussing. In terms of the actual cinematics, Terran Gregory and the team involved, including the voice actors, stated that they were still deciding on the exact delivery, details, and individual character beats for 9.1's finale as the patch was in the works long after launch content had been finalized mid-Pandemic, which was after he had been dropped. To say nothing of changes to SL as a whole, which they maintain was always intended to be this long, but obviously we all know better.
The Sepulcher is such a vague and non-descript term, not counting the reality that it's named for an actual real world concept, that we don't even know if Zereth Mortis as it stands right now was intended from the beginning to be what it is now. It's an ill-defined location Macguffin. It was also introduced at launch, not in 9.1, via the Primus.
The hoops you jump through to give these hacks a fair shake is legendary when they've routinely proven to be pretty bad at their job.
As it stands, if there's ever any actual facts supporting that Afrasiabi having Sylvanas torch Teldrassil was a malicious hack job, how do we reconcile that with Shadowlands taking an almost 180 on her character? Can you at least answer that?