They're quite good, actually. They have access to the ranged promotion tree, which for my money is the best promotion tree in the game. If you can get a Keshig with four promotions (Volley, Arrow Storm, Garrison, and Incendiaries), these things can shred both armies and cities. Though, it is unfortunate that they don't get Genghis' Mongol Horde bonus. If I were the devs, I'd patch that in because it really doesn't make sense, since they can benefit from both the Chivalry and Feudal Contract cards (non-stacking), so it kind of counts as both unit types.