I always have mixed feelings about byzantines tbh. They are not a bad civ by any means, but they aren’t particularly good at anything either. I think they are supposed to be a civ with a broad tech tree, very flexible and powerful in the late game, but they are missing a few very important techs:
-No bloodlines and no blast furnace hits really hard cavalry, especially in late game. Sure, you can still go knights in castle, but then what? Cavalier (or even worse paladin) without bloodlines and blast furnace? That’s a waste of resources. Camels can still work fine in castle, but in imperial they are just garbage. Moreover you have cheper halbs, so why waste res in something like heavy camels?
-No parthian tactics and no bloodlines means that cav archers are no good.
-No siege engineers is kinda bad for onagers, but I think that’s ok given that they both siege ram and bombard cannons. However once again, their siege is good but not amazing by any means.
-No blast furnace means subpar champions. They got handcannons at least, so i guess it’s fine.
-Greek fire UT is useless in practice. This needs to be reworked. Maybe something like fire ships move faster.
So what’s left? Arbalests and cheaper trash, which means that in practice byz are played like an archer civ.
And what about catas? Even with upgrade cost reductions, they are barely seen. Everyone says how good they are, yet nobody uses them. The truth is, while their stats are good, they are still too expensive to both produce and upgrade for what they do. Plus they are produced only by castles, a further bottleneck.
I would try to give byzantines blast furnace, so their melee units become more viable in the late game. Right now they are played like an archer civ in practice. This also wouldn’t change anything until imperial, as they will still struggle with their lack of eco bonuses in the early game.
Would this make they cavalry units OP? I don’t think so. Camels are discounted, but still lack bloodlines, which makes them not that great. If needed, discount can be decreased to 15%. Paladins become more viable, but probably won’t be seen in 1vs1. They are already very expensive, and missing a critical tech like bloodlines really hurts. If catas damage output get too large, I would just tune down a bit their attack speed, though tbh I don’t think that would be necessary.