Yesterday I had fun in a party doing "Lost Vale" quests. Everything worked fine and all quests gave their reward. However after leaving I noticed that some other quests that I had open for a longer time had reacted to it. From the "Visit all devotionals" quest I had collected all the quests to defeat all the Cabalists (e.g. Temna etc.). And suddenly those quests had all changed to "Talk to to e.g. Eastmarch Caretaker about the fall of e.g. temna". I went to the first and got around 50 K XP and the warning that the Cabalists have ways to return. So, I thought that those devotional quests were connected to the Cabalists in the townsieges that are going on. I never killed any cabalist there. In Lost Vale the defeat of those guys happened while refighting a memory fragment - like re-fighting an old battle that originally already happened and is past history, and winning but then returning to the present so nothing actually has changed...? Are the Lost Vale battles with the Cabalists supposed to trigger the "defeat the Cabalists" quests from the devotionals?
Each quest just says to kill that particular cabalist. It doesn't matter where you kill them. Pretty sure that is working as intended.
Adam Crow is correct. The Devotional Caretakers task you with defeating Cabalists. They warn you about sieges and want you to defeat any Cabalists that appear, but they don't lock you down to "Defeat Cabalists in Sieges." If you happen to find and defeat Cabalists somewhere else, then you continue to have the support of the caretakers!