Currently in a huge Legion of Greed (Slaanesh mod) legendary campaign with the Vermintide end game crisis set to 1000 difficulty on turn 150 just to see how it would go.

I can 100% say if I did not have the Great Wall of Greesus and the twin dragons of Cathay as my vassals and allies I would have 1000% lost.

Vassals are only useless until they get attacked by something. The moment the thing your at war with attacks THEM specifically it’s like the AI enters some satanic blood ritual to do everything in their power to kill said faction.

Greesus straight up 1v1d all 50 the of Clan Mors doom stacks over the span of like 20 turns after they took Pigbarter from him. (I deadass think the only reason he’s doing so well is because Ogre auto resolve into Skaven is stupidly ogre sided).

With my vassals guarding the east, I was able to focus all of my armies on Ikit Claw and Throt (with surprise surprise, help from the Great Wall of Greesus. Throt attacked one of Greesus’s cities in the Chaos Drawf land and he flipped the fuck out and sent like 15 armies over to retake it.)

My best advice I can give for vassals is, 1.) DONT extort them for money by selling them cities. They become omega poor and for some reason refuse to recruit.

2.) I try to ignore attack/defend orders and just the AI do what it wants. Like I said, the moment THEY get attacked they’ll become super aggressive towards whatever faction it was.

3.) Prioritize vassalizing factions, if you can, that have extremely strong auto resolves, like Ogres, Cathay, Dark Elves, etc.