I don’t disagree. But, if I recall, the person who wrote Lorash specifically said they forgot all of that. Thus, we have Lorash’s reasoning being his parent’s exile, and also that High/Blood Elves can live over 7,000 years, now.
Chronicle at least frames it as an act of compassion. Not just on Malfurion’s part, but on that of all the lowborn Night Elves:
In the end, the other night elves could not bring themselves to sentence so many of their brothers and sisters to death.
Emphasis mine. The lowborn Night Elves not only viewed their Highborne kin as brother and sister, but also seemed to believe they’d have been able to execute the Highborne with relative ease, but chose not to.
Perhaps Dath’remar in and of himself was. But most of the surviving Highborne were not the top tier in terms of power. Most of those went down with Azshara, and either fell in WotA, or became Naga (or satyr). Elisande was probably the only upper echelon Highborne left, and maybe Tortheldrin, if his rank of Prince was anything to go by. And they were both locked away in their respective cities.
Shandaral is described in Chronicle as just an outpost, even in the times of the Empire. It also says they were completely cut off from both the Night Elves, and Dath’remar’s Highborne.
They were all bubbled up, and quite content in thinking the rest of the world had burned down around the barrier. It would be quite some time before they ever realized anyone had survived outside of the bubble, and by then, they were too dependent on the Nightwell to travel far from it.
You would think that. But, somehow, Chronicle still describes Shandaral as totally cut off and isolated. Likewise the Shen’dralar never left, no matter how bad things got. Idk why or how all the Highborne managed to seem to forget how to teleport
All the rest of your suppositions on a civil war doesn’t match up to what we have. As I said, the lowborn and Malfurion seemed quite confident they could have executed the Highborne. They just didn’t.