The WRE don't get Cataphractii, Clibinarii or Eastern archers. Instead, they have Praeventores (think arcani), Sarmatian Auxilia (fast, reliable cavalry) and Scholae Palantinae (expensive and not great cav).

Sarmies have the advantage of a lower tech requirement and quicker recruitment though. They're also cheaper. It's also strangely satisfying to butcher barbarian with barbarians.