I made a similar less extreme propose Civilisation crest on generic units
They should at last change it in that way that the units of different architecture sets are technically using different sprites even if they are practically the same so they can be modded to use different sprites without having to make a data mod.
But yes, seeing white European soldiers in Aztec or Ethiopian armies just looks wrong.
They could change the skin colour at least.
Ships have unique sails already so that wouldn’t be something completely new.