Eastern horse has so many reasons for no one to ever use it. First of all, the eastern horse has a difficulty requirement of 8 riding. Hardly anyone levels riding skill up this high. Only dedicated horse archer/xbow or dedicated light cav can even use this horse. It is the only item in the game that requires 24 of a stat and 8 points in a skill to use.
The eastern horse has speed and maneuver stats that look tempting. However, there's no reason for light cav to pick it over a courser - speed bonus is king when you are couching or lancing. The arabian horse is slightly cheaper with 4 more maneuver and 3 less speed. Seems like a viable choice... but then you look at the other stats. Less HP and less armor than a fucking sumpter horse. Less charge damage than a rouncey. It is so weak that it will die when you look at it wrong. The donkey has equal HP and 1 less armor.
Should the eastern horse be buffed? Even with better stats, I doubt that would convince people to go for a build with 8 riding. For the vast majority of the population, this horse isn't even possible to use. Maybe reducing the riding cost to 6 or 7 and tweaking other stats to bring it up to parity with the arabian? Overbuffing could lead to HA supremacy, but I think that it should be reworked into an equal alternative of the arabian horse.
As it stands now, the eastern horse is never used. It fills no niche role. The only thing it's good at is dieing.