Amirdrassil is definitely the new capital, Mathaelar. I don’t think anyone is denying that part. I think the questionable part about your headcanon is that you are claiming that they won’t continue to have a presence in Kalimdor. It’s pretty simple minded to assume that a group of people can only be in one place. The Worgen (who had it much worse than the Night Elves, by the way), moved their home to Darnassus but there were still plenty of them running around other parts of the world