I have 3 issues regarding confederation in Mortal Empires campaign; one of them is probably a bug.
1. I played Rakarth and confederate Morathi. It soon became clear that I could barely use her, because she recognized all my provinces with a Chaos Corruption, and I had to leave her to stand at the sea. Is it not wiser to console the chaos spreading of Morathi when another faction of the Dark Elves confederate her?
2. The following problem appears in almost every Mortal Empires campaign I had played. At the beginning of the campaign, Naggarond's power increases, so the Dark Elves manage to hold on, even though almost everyone around hates them. But later in the campaign, Malekith confederate almost all the Dark Elves factions, including Hag Graef. this situation causes Naggarond to hold two distant territories with a crazy distance between them: one in the northwest corner of the map, the original areas of the Dark Elves, and one in the southeast corner, the former territories of the Malus. Then, Malekith had to split his forces between two areas that were far apart from each other at the greatest distance that the campaign map allows.
What happens is, that Malekith does not always succeed in this difficult task, and he becomes easy prey for his many enemies. So sometimes we see that Malekith gets stronger at the beginning of the campaign, but then suddenly crashes.
I would suggest a very simple idea: to cancel out that Malekith starts the campaign with a military alliance with Malus. This way Malekith will not contact Malus, and will not be able to confederate him, just as it does not confederate The Blessed Dread, usually.
3. The third problem is apparently a bug: I played with Clan Skryre, and confederate Clan Moulder. I got Throt The Unclean, but with a loyalty meter. is this a bug? legendary lords never have a loyalty meter. not even when you get them through a confederation.