That’s not even really what impresses me about the AI in that game. It’s how it interacts with all the diplomacy, like aggressive expansion, allies of allies, rivals, etc. An ally knows when it’s time to start calling the alliance quits if you start competing over territory or goals with them. For instance, Castile may be willing to ally France, but that alliance might come under strain if France is being dangerously aggressive, if they’ve taken a lot of territory in Iberia from Aragon, or both countries start competing heavily over Italy.
Or maybe not. If the alliance is long-standing and you’ve helped them in several wars, that can really help offset it. And speaking of helping in wars, the AI knows the difference between just agreeing to the Call to Arms versus actively helping in battles, which in turn earns you Favor which make them more willing to help you in your own endeavors.
None of it is rocket science and of course it still has its limitations, but does it ever kill most other strategy games for me. When I get a random war declaration from an ally in Civ5/6 or it’s from someone with literally no capability of even reaching my borders, I just shake my head and quit in disgust.