Where do people get the idea that cataphracts are overpowered? Let me go through some things:
They have the second most expensive elite upgrade in the game, after war elephants.
They are more expensive than knights.
They lose to paladins.
They have low pierce armor, and die to arbalests, hand cannons, heavy cavalry archers, and all UUs with pierce attacks. Also heavy scorpions.
The Byzantine UT is the most expensive in the game.
Byzantines miss blast furnace.
If anything, they should get +1 NORMAL armor to balance them a bit. As of right now, my main strategy as Byzantines is usually to mass trash with archers, maybe switching to hand cannons in imperial, and having siege and BBTs as support. Elite Cataphracts have their use, but it seems limited, to be honest.
Now Boyars, they need a boost. I liked them when they had 16 attack.
i think you have have a strange Picture of bycantines, especially of cataphracts:
They have a expensive, but extremly effective elite update: +50 HP, +3 attack
They are more expensive than a Knight, but this more expensive is just +10 food, that s nearly nothing in late game, only gold is important; and yes 75 gold is much
They lose vs Paladins, but have cheap halbs and camels. generally you use a Combo of halbs and cataphracts, sometimes also camels.
They have low pierce armor, but have cheap skirmishers, you can make a trash war, or defeat the cavalary archers with cheap halbs and camels, only Hand canoneers are a Little Problem (because of that turks are the best way to defeat them)
The Bycanite UT is the most expensive, but extremly effective; halbs get senceless vs cataphracts, and sometimes the +6 attack helps you to win vs Paladins, if they are really stupid.
the blast furnace for bycantinians would be great, but would make them OP, especially in trash wars.
if you play just cataphracts, thier use is limited, but if you use a Combo of trash units (maybe with some camels) then the cataphracts are nearly unstoppable. I think +1 armor wouldn t be bad, but they are already strong enough with thier huge amout of possible updates and effective bonuses.