I too hate it when my vassals' holdings are all wonky. I don't mind them expanding and contracting, I just wish they were more or less contiguous... I have a lot of trouble understanding even basic stuff like the realm of some double-duke uncle spread over bits of Scandinavia and Britain. I wish there was a button to highlight vassal holdings in your own realm, because the little thin and thick lines just don't do it for me. Particularly since I enjoy having large vassals (with the retinue system and mercenaries, I never seem to be in actual danger from my own vassals, and they handle a lot of the management - as they're supposed to!).
Usually results in me doing a mass-banishing to clean house, which means tedious revolt-crushing, and then I get bored and restart. I have 360 hours on this game and I've never yet seen the golden horde or incans! Playing raid-happy norse probably doesn't help, as it requires considerable micromanaging (in return for constant mad loot).
I finally let go of my absolute-cognatic (Better Gender Laws mod) Empire of Scandinavia because I couldn't get rid of the -50 "Wrong Gender Law" penalty, even after two generations of rulers, and even new, FEMALE, vassals were complaining. It might be because Sweden is still agnatic-cognatic, but I can't *fix* that without having positive relations with all vassals *and* being a female ruler - and my female ruler died of stress at like 35, and her successor popped out 3 sons before any daughters.
Not sure if the mod is slightly bugged for multi-kingdom domains or what. Ah well, this time I just started in Ironman Gotland with a simple mission:
* Stay loyal to my liege the King of Sweden as long as at all possible, ideally helping him form the Empire of Scandinavia
* Failing that, find some other liege to pledge to
* Just keep playing long enough to see the freakin invasions! Which means not going conquest-happy. Fingers crossed...