Assuming you have free investiture, they are by far the best vassal type. Their income level is higher than mayors outside of sea provinces, they almost never rebel, they give you piety when you appoint them, and most importantly, you have absolute control of their culture and opinion. That means that for different cultured conquered territory they are the only logical choice.
It just feels weird to have a massive empire ruled entirely by bishops. I don't think this is historically accurate, since I don't believe any prince-bishops exist at game start.
It just feels weird to have a massive empire ruled entirely by bishops. I don't think this is historically accurate, since I don't believe any prince-bishops exist at game start.