There are really a lot, like a lot of unique units you could give to Byzantines and that is one. Personally I would make the cataphract a regional unit since cataphracts were in origin an Iranian/Scythian thing and many people other than Byzantines employed cataphracts in the middle ages. Replacement could be the Excubitor/Tagma, a palace guard instituted by Leo the Thracian in the 460s and turned heavy cavalry around the 750s by Constantine V. Not sure what the role could be but we don’t have a cavalry unit that strips armour I think? Anyway you can find something and knights could go so you have cataphracts at the stable instead. I know knights and cataphracts do not have the same role but that’s exactly why you wanna add regionals and not a pseudo Knight reskin like the hue Huang is.
