Vills are not a fighting unit so it is not important if they look different for civs, just like monks and tradecarts. Viewers have indeed a better and easier viewerexperience if knights look the same for all civs, how vills look does not matter in fights, so having different graphics there is not an issue.What makes villagers so special.
Therefore I see why army units could stay identical and I don't see why different graphics for vills affect anything ...