With leader/civ mixes, what about this:
Churchill of the Sioux Empire
Traits: Charismatic (-25% XP needed for promotions)/Protective (Archery, Gunpowder units begin with City Garrison I (+20% City Defense) and Drill I (1 extra First Strike Chance).
Unique Building Totem Pole (More XP for Archery units as EXTRA Barracks)
Then, Archery units will receive extra XP, including Barracks bonus, extra promotions from Leader, fast level-up!!!
and maybe the Sioux uu might even be an improved Archer unit because of the ub