I get you want to promote more a certain gameplay style and maybe be a little more realistic about that era, but this is a game after all and I think it should support as many playstyles as possible. So, I think when cultures have the Staunch Traditionalists in their traditions, your vassal's AI should play the pre-Royal Court gameplay and prioritize Cultural conversion over Cultural acceptance. Right now, every land that does not have my culture, has a Duke of my culture and instead of trying to meet the demands to culture covert the area everyone of them and their mothers are promoting cultural acceptance and they try to meet the demands to culture covert themselves. There were some vassals that converted their lands at the begining of the game but they were not too many, for guys that value their traditions so much and now, since the acceptance is over 50% they have stopped even trying. Staunch traditionalist feels like the go-to option if you want to try a one-culture, one-faith playthrough but right now I don't think it plays like one. I am thinking to do some strange things to lower the cultural accepance that are a little bit exploit-y and definitetly not streamlined for a Staunch Traditionalist gameplay. (Since all my vassals were of my dynasty too, I have released some of the lands I have conquered -I have the By the Sword tradition too and it was easy to conquer a lot of land- so I can earn more dynasty points. Obviously they too, as free rulers, prioratize cultural acceptance over conversion even when they border my culture.)
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