You can mod your game to any style of your liking. There are many mods and one I am currently using lets me play campaign as timurids and mongols and BOTH use the rocket launcher.

When I first got the game I had your exact same outlook as far as unit generics goes. England and france have very very similar units. 5 or 6 factions have equal feudal and chivalric/insert special name here knights.

But its the faction specific units that make the game fun to play.

Trust me, this game is far from perfect, and the AI is a bit of a step back from rtw, but its still a good game, and if you play it more I guarantee you will almost certainly learn to like it more.