As the titles says, can said rule exist?
Seeing priests and popes richier than every empire combined is quite laughable. Especially because the player can imprison their priests realm, banish them and immediately become rich. The other problem is when they're at war and they can spam mercs and easily win every war (If the pope would want it, he could conquer all the world in 3 years).

Is it possible to lower their income, or make it easier for them to lose it over time in some way?


Afar from that I also have another question since I can't normally comment I don't know why. How does your advantage rule works? Does it boosts the effects of advantage in war (e.g. If terrain advantage is normally + 5 with your rule becomes +10/15/20 (depending on the chosen sum)), or it is just a flat +X to the player/AI army no matter what?
I'd like to be the first option because in this way I could push the game to value more the advantage rather then the number of the army and number of MaA.