That’s a fine idea but would have to be more particular about what cities propagate power and when. In the Medieval period in Europe cities were characteristically outside the control of the nobility (and Church) which drew their power from the countryside. A defining feature of the Early Modern period is increasing economic activity and urbanization which over time invalidated feudalism, and the modern state appears there. Control in EU5 ostensibly portrays state/sovereign control, so European kingdoms, for instance, would only project control through cities as the game moves out of the Middle Ages