From simple to complex, in my opinion, has always been the right way. It is impossible to start from scratch, without resources, a team and everything else, to accurately recreate or surpass Europa Universalis VI.
I have read and noticed that you are planning or at least thinking about implementing the mechanics of science. I would like to propose a simple and authentic way out: let the AI learn not certain discoveries, but abstract ones, like certain power-ups. So the gameplay will not be limited to certain historical periods and the player can simulate absolutely any event from the capture of Constantinople to the collapse of Yugoslavia.
I'd like to suggest a small correction: I don't think it's correct to equate water tiles with a crossing to land tiles in everything from "army" movement speed to "ownership" itself. If you put "army" for "military potential" or for "power potential", although I don't know how you could implement this, it would be possible to allow more than one AI to "own" a water cell. Or perhaps we could slow down the expansion rate and limit the ownership of water tiles to the distance from the ground tiles owned by the AI. Here, in a word, if technology appeared, it would be possible to simulate the colonization of America, because now any country that has got a way there can colonize it.
You can see in the attached screenshot that I also used regular non-movable water tiles as mountain ranges. It's more about the textures or color of these cells than about adding new states, but the mountain cells are probably the important thing.
Well, and some cosmetics. I don't know if you use predefined lists of names, but don't we have name generation tools? I know one of these: the use of the words of a certain language, the names of cities and regions as material for a method of creating new words, very similar in structure and sound to this material, but different from it. If you are interested, I can describe in more detail. Then it seems to be great if the AI had certain titles coming from the parent countries. For example, here in the screenshot I have the Crac Empire. The first of the empires. Why not add this "Crac" before or after the name of the state in honor of this. Far from all, only those that rebelled from this country or neighbored it, being of the lowest rank, and then reached the same rank?
Well, the last. GIVE THIS DOWNLOAD AND SET MAP SIZE 20000x20000
