The next Pope will be Catholic.
That's 4 built holdings in a span a little over 100 years. It cost 2600 gold just to create those holdings themselves, and perhaps even more spent on upgrades. Republics are overpowered. Just have everyone start as a castle. No exceptions.*
Just an FYI: I'm playing a slightly modded version of the hotfix someone posted recently. I added titular empires of West and East Rome, but I didn't mess with holdings so super-Venice can happen anytime.
*I lied. Exceptions should be made for Rome, Constantinople, and Mecca. Add a temple holding for the head of the Catholic, Orthodox, and Sunni/Shiite religious figures. This way, there'll be a (small) court for the big 3 religions, and the player will be able to convert by inviting courtiers to tutor their children, so they don't need edit saves to convert. I also noticed that the Pope starts Pagan, while the Patriarch starts Orthodox. Is this a weird glitch or WAD?