Yeah, I think it could really use a small HP and armor buff.
I think the maneuver and speed are spot on for a horse whose specialty is, essentially, agility. Any more maneuver or speed and the horse would stray into the realm of OPness. Plus the problem here is that the Champion Arabian Warhorse dies too easily.
One of the advantages of an agile horse is that it is difficult to hit if the rider maintains a relatively unpredictable pattern of movement, and is wary of incoming attacks and actively dodges them. Thus, compared to the other high-tier, unarmored horses (Destrier and Courser), it should have the least HP.
At the same time no horse that's that expensive and has had that much time and effort put into its looming should die in two or three shots. It's just not fun, and its unfair to the horse's owner (and the horse, poor guy). SMALL HP BUFF--though to be honest I wouldn't mind nerfing it into the ground either.