This is the Empire; King-level vassals are Urban Feudal and need to be called to arms.
Mostly I'd advise just not worrying about outlying unprotected province income; you lose money but it's filtered through multiple layers and barely matters. Fanatic revolts can be trouble but aren't common enough to be overwhelming on their own and the Urban Feudal vassals can handle the rest.
Mostly I'd advise just not worrying about outlying unprotected province income; you lose money but it's filtered through multiple layers and barely matters. Fanatic revolts can be trouble but aren't common enough to be overwhelming on their own and the Urban Feudal vassals can handle the rest.