Not true. The Mandekalu Cavalry don't have the -33% combat strength against cities that Knights do. Since this isn't a promotion, but a lack of penalty, it does return when they are upgraded to cavalry.
Edit:Ninja'd by ideolect! The bonus against cities isn't really useful, since siege units do most of the work on cities. Atlatlists are also simply cheaper versions of archers (that can be built earlier as well).