Get rid of the fake "unit variety." The player should be able to recruit any certain number of troops as long as he has the resources. What that means is that you should be able to recruit 177 men, 98 men, or even 62 men. These will be the player's "basic troops." The player should be able to outfit them with supplies he purchases. So that means armor, weapons, rations, and housing. These troops should perform based on their military training, their commander, and their active service history. The armies need to feel like YOU MADE THEM.
Diplomacy needs to change. There should be more ways to affect the relations between two countries, aside from just waging war on one and not the other. There should be combined arms practices, joint military operations, political deals, marriages, sworn brotherhood banquets, celebrations after defeating a mutual enemy, backstabbings, sale of land, purchases of land, etc. Even the internal administration of the player "empire" should change. It no longer feels personal or realistic for the player to control such a vast empire. I suggest CA take the Crusader King's route. The player will play a "dynasty" of characters, with succession, death, marriage, concubines, the whole shabang. Conquered territories should have to have local rulers when the player's character leaves, if he chooses to even personally lead the army himself. Ministers should grow bold and challenge the player's sovereignty if left unchecked. The player should have advisers, master of coin, master of intrigue, etc. These should all be included.
The map needs to feel compact, but relevant. In Rome 2, CA took out all the gold mines, the farms, the little things on the map that made it relevant. What they added instead were choke points, narrow corridors, and more fake "map." Each part of the map should feel like it matters. The yellow river or the yangtze should play crucial parts in the game to control rice cultivation, essentially blocking access to rations from your enemies the more contorl of it you have. Farms, silver mines, gold mines, tea plantations, silk makers, paper makers, should all be interactive destinations on the map. Most of all, the map should BE ATMOSPHERIC. It should make you feel like you're a part of the setting, and not just an empty, ugly, piece of cardboard.