I have not played any TW title after Medieval 2, and from this perspective your statement "combat is not actually 1v1. Just the animations only support 1v1, so that's what things look like" does not make any sense.
Or rather it does makes sense but the implications are dire.
To elaborate: your Statement implies a disconnect between the battle calculations and what is actually seen on the battlefield. That the combat is not actually based on the individual soldier but instead determined on an Abstract unit Level.
Having not played any Warscape TW title I cant judge if this is true or not. But for a Total War game it seem like a very stupid idea: in Total War games there is no neat 1 unit on 1 unit combat. A battle model based on the individual soldier is the way to go for a Total War game.