Why? Byzantines were always considered a good post imp civ.
Hussars, cheaper halbs and skirms, paladins, BBC, FU arbs, onagers, SR, the tankiest castles in the game…
There isn’t a thing that they can’t do, and their cataphracts ones you get them going can shred everything to pieces.
They may lack BF and BL on their knight line, but onestly, paladins is often a better unit, even if not FU, than generic cavaliers.
Compare them to Italians cavaliers for example, that are considered decent and generic. Byzantine paladins will have the same attack of italians cavaliers, and 20 more HP, so they’ll beat them. They’ll also have 1 PA more, making them way better vs archers.
Yeah the price of the paladin upgrade is high, but if you are in a TG with trade it’s not a problem.