I wonder at how different our playstyles are, I never get these rampant council demands, I've even played as a vicious Carloman who imprisoned and executed his own wife and children.
Do you use scheme to get vassals out of factions? do you use send gift to get vassals about 80(to get them to leave a faction) or 60(so they never join one in the first place)
Do you educate vassals as often as you can so they grow up to like you?(and have less rebelliously inclined traits)
Do you put powerful vassals on the council so they are more content?
Do you on occasion take intrigue focus so you can focus-fire on a single powerful vassal so you may imprison/revoke his titles.
Do you try to ensure your rulers focus on a strong centralized desmesne and high martial for more personal troops or ensure your rulers have high diplomacy so people like you more?
I know much of what I said are things that require getting farther than 30 years in game, but I'm pressed into thinking you must be heavy-handed or something. I never have to take council ultimatums more than once a reign(twice if I'm unlucky or my ruler is especially a bastard trait wise)
and as above, betrothals with vassals are non-aggression pacts and they won't faction against you(although you can't revoke their titles either)
I hope this post doesn't seem accusative that you're a bad player, I just wonder at how different you and I must play