What? Murchad is the only decent HA and even he is stupid to keep at it. He is so much better than that class lets him be that its ridiculous
Duke_Of_Disco_ATS, Mongorian_ATS, whatever his name is now.. that dude is really good at the class, probably the best regular HA on NA, though he doesn't play very much. He would get tons of kills every map. If Rohypnol specced into HA he'd probably perform just as well as he does as HX, its lower damage but the accuracy is the same and has a higher rate of fire. This makes it really good for shutting down HX's or ranged players.
I did a gen or two as HA, and its really not that bad. Its just difficult and takes some practice to effectively lead your shots. Eventually they are gonna add in momentum of your horse affecting damage you do with mounted ranged weapons, which will buff the class.
You should focus on suppressing light cav and harassing other ranged classes with a maneuverable horse like an Arabian. This lets you juke enemy cav and ranged very effectively while letting you slow down when necessary to get the best accuracy, but generally you need to stay moving so you don't get lanced or shot.
If you are using a horn bow and tatar or especially bodkin arrows you are hitting pretty hard trust me, unless they are heavy armor with high IF. The class simply isn't that strong against heavy infantry and cav, but is great against lightly armored horses and players and the horse lets you choose who you fight. Just get good at leading your shots, juking ranged, and killing as many horses as possible. Once you get better aim, you will be able to shoot the rider pretty easily and you will shut cav players down hard.