Underuse of cavalry in the roman army

[Domen]

Hungary is in the east bro.

Hungarian army in the 15th century was much more similar to German army than to Byzantine army.

So your purely geographical distinction of East and West is somehow fallible here.

Hungary was also in the sphere of Latin Christianity, while Byzantine Empire - Greek Christianity.

And shields on cataphracts were common.

"Western" - as you call them - knights also used shields. Even after the development of plate armour.

I would say that High to Late Medieval Russian cavalry was quite similar to Byzantine cavalry.