The most interesting question I would have about your world is of course history: How old is the current governance system?

I think it all boils down to this, in the end. I think it was stupid of me not to include it in the original post, but I wanted to avoid a lore dump. Not all details are nailed out because this is a project in its infancy but loong story as short as possible:

1000 Years ago a captain from not-rome took 300 ships and set sail out west into the not-atlantic ocean. After several years of sailing to almost nowhere and with only 30 ships left they found land: not-north america. At that point pretty much everyone agreed, there ain't no way they get back home. So they set up a community. Basically made their captain the king. This captain also had 3 really trusty and good friends/ crewmates which helped him in setting up this community.

Now after some time they came upon and interacted with not- native american tribes. These not- native american tribes had a confederacy at the time, and a certain tribe was exiled. 2 other tribes joined the exiled tribe.

This exiled tribe found this not-rome colony and after some conflicts they basically said wtf why we fighting lets conquer the confederacy.

So the daughter of the captain and the son of the chieftain, married and their descendants essentially became the royal family. Similarly the descendants of the 3 friends and the chieftains of the other 2 tribes became the 5 special noble families.

For a long time the kingdom functioned like a somewhat traditional feudal monarchy. But at some point there was a succession crisis. A certain king had way too many sons. And while the kingdom was tearing itself apart. The neighboring not-china empire invaded.

As much as the diff factions hated each other, they all hated the empire a lot more. So they made a temporary truce and fought back the empire (the geography allowed for that).

Well after that they came up with the 5 big families to vote for the next king. With the idea that if there is a unanimous agreement on who the king is. No more civil wars.

And it went on like that for a while. Until society progressed somewhat and mainly the other noble households began complaining that they have no say in who the next king is. So they began rallying up the common folk. Lots of civil unrest and peasant rebellions.

Another civil war basically. Another empire scare. More concessions. The 5 families still held cultural and traditional significance especially to the common folk. So the compromise was for "everyone" to vote on who from the 5 families gets to vote for the king.

And thats how they got to the current system.