Battania stayed about the same size on my run past day 300. Khuzaits got much of their land taken though. I don't have a problem with smaller factions conquering the world as it's pretty realistic IRL if you look at the British, Roman empires, how a smaller faction was able to colonize India or Imperial Japan and Mongols conquering China.
I do have a problem with the rate of the imperialism though which should ideally be much slower or take up many more years, decades at least to conquer most of the map.