#1. Their buildings fall easier to melee units, not to siege. They get their HP buffs for free. #2. They have been given treadmill crane
I kind of get you here but I have a better idea
YES. Give them bloodlines but in a different way. Logistica tech gives +20 or even +30 HP to all mounted units along with trample damage to cataphracts. So, they are incentivized to go to the imperial age.
Note : giving them +20 HP means they will still lose to a generic Paladin or generic Heavy Camel or generic Hussar 100% of the time since they lack blast furnace.
Exactly? What is the point of a ‘late game’ civilization if you can’t even produce fully upgraded units except for archers?
Infantry lacks blast furnace. The spear line and skirmisher discount is irrelevant in the late game.
In the stable, they got Paladins, Hussars and heavy camels which appears to be as good as a Persian stable but in reality, they lack bloodlines and blast furnace.
Compare this with other late game versatile civilizations like the Spanish for example: Everything from a Spanish barracks is better than its equivalent from a Byzantine barracks. Same for stables.
As for archery ranges, the Spanish lack any upgrades for the archer line but their heavy cavalry archer (nobody uses this) and hand cannoneers are better. As for the Siege workshop, they got the same techs but the faster firing gunpowder units affects their cannons which again makes their siege slightly better. Their monks are maybe slightly better (but not by much).