Promotion is usually on a unit with weaker than normal stats, and with promotion they are stronger than normal. However bosniak base stats is good enough. No need for promotion. Currently the bosniak shipment from certain civ is just broken. Completely turn this game around, from disadvantage to advantage.
Also having promotion on strong multiple pop unit is just not a good idea. They are individually so strong it is very easy for them to kill a few skirms or any weak unit and get fully promoted, and even harder to kill. Promotion should only be on one pop unit like irish brigadier.
German 7 bosniak card is simply broken. 2000 coin for 7 bosniak is 285 coin each. It is absurd, and it enables more bosniaks to be shipped with each card in the future. This card need to cost 1500 coin at least.