You guys also seem to see the Middle Ages as clear cut rules, however there was no internationally recognized let alone enforced law of succession.

Merchant Republics in Italy did exist (one Dodge of Venice lost his head for trying to make himself king of Venice), the Byzantine Empire was in theory at least not a hereditary monarchy, and the English System believe it or not sometimes had WOMEN inherit (I.E Queen Matilda).

When there was something like King's Daughter vs King's brother you could have a reasonable expectation that a civil war would come, you could also have a civil war if the king had more then one brother and died childless, sometimes there would be civil war with a clearly legitimate hier to the throne and a person without any inheritence claim (I.E in the Byzantine Empire John Contacuzenus took the throne without any claim to have it through inheritence).

There is Medieval history backing the idea that you should chose who inherits the throne, and medieval history suggesting you should have no say in it.

From a gameplay perspective though I like the way CA did the inheritence. Sometimes kingdoms got cursed with the worst possible leaders imaginable, and the will of the people, or even of the king doomed to be succeeded by these jerks had no authority to change it, and sometimes like in the game kings might not notice that they had bad sons as hiers, for example Michael Paleologus simply didn't notice that his son Andronicus II had no governing skills.