You're seriously underestimating the strength of being insanely fast at will while still having the maneuverability to dodge most horses.
as rusty posted above, i understand you can move faster, but when you go to turn, you must slow down like a courser to make the turn, and the arabian will catch you at this point and have its way with you. The horse is by no means "good" at anything, you ever heard the saying "Jack of all trades, Master of none". Well thats this horse, and 8 riding makes it even worse, i believe the horse's difficulty should be 7, even 7 is a push for cavalry as 90% of the other horses can be rode at 5 riding.
Also dont get me started on how weak this horse is, its survivability sucks, just flat out sucks. Atleast the Arabian and courser can take a few hits and not seem like they are frail and on the verge of death at all times. It has nearly the same stats as a Donkey by only being 1 point off.
Donkeyhit points: 80body armor: 5difficulty: 0
speed: 24
maneuver: 27
charge: 5
Sumpter Horsehit points: 90body armor: 10difficulty: 2
speed: 33
maneuver: 37
charge: 9
Courser
hit points: 100
body armor: 18difficulty: 6
speed: 46
maneuver: 41
charge: 15
Arabian Warhorse
hit points: 100
body armor: 10difficulty: 7
speed: 41
maneuver: 48
charge: 13
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Eastern Horse
hit points: 80
body armor: 6difficulty: 8
speed: 44
maneuver: 44
charge: 11
My opinion: The reason the Courser has 100 health but 18 body armor is because while this horse is in a full gallop, a striking arrow will cause massive damage to the horse because of the momentum, so to balance this horse it needs almost double the body armor of the Arabian. The Arabian is stated weaker, but its also slower, much slower. So this horse's armor is lower to keep an average between the two, so one horse is not inherently stronger then the other, it just has different abilities to perform, ie. Faster or turns better. Yet the Eastern's stats make it faster then the Arabian, almost as fast as the courser and it as 3 times less body armor, and 20 less health, making it on average much much weaker. From personal experience, i dont think my horse has ever lasted through the round, i get about 2 mins in and our pinpoint archers shoot me down, leaving me running about on foot like common rabble, wondering why i spent 8 riding to get a weak horse when i could have spent 5 and rode a plated charger.