I can understand why Eagles and Fire Lancers have this armor class for balance reasons. Because the first one doesn’t share typical cavalry weaknesses to Monks, Pikes, and Camels, and the latter isn’t as weak to arrows as pikes are. So, they have different counters instead.
However, the issue is that these two units are nothing alike. It’s counterintuitive to give these two very different units the same exclusive armor class. Whereas Huskarls and Ghulams are much more similar to Eagles than Fire Lancers are. And unlike Eagles, they don’t take bonus damage from the militia line, and they deal bonus damage to Eagles.
I don’t currently have any proposal, but Eagles and Fire Lancers sharing the same armor feels as awkward as if camels and ships had the same armor class.