this is all related to siege defence.
if catapults worked on the walls, instead of overshooting everything in existence. What should focus on the battering ram giving the defence an actual solid chance of resisting a siege that doesn't have trebuchets. Also that cities and castles cannot manage food stores properly so sieges cant last a month regardless and you cant keep a garrison because of the food issues.
^^^This is another huge reason. AI are terrible at defending in sieges from my experience. Realistically storming a fortifies city/castle should be insanely costly and attackers should take major casualties vs the defenders.