I don't really want to like "downplay" Ryuma, but I don't think Ryuma is supposed to be that important because Oden and Kaido both hype up Joyboy only. And I think we know the Kozuki were the ones who originally closed the borders, so it doesn't seem like it was Ryuma lead the country either really.
Also, the Gorosei in Egghead don't really mention Zolo looking like Ryuma, though this could come up later ig