As said before, with the speed bonus courser gets onehitted often from throwing weapons or arbalest if the rider isn't extremely careful with his riding speed and positioning. I've had situations where 1 arrow has left approximately 1hp to my champion courser. I wouldn't call that OP. Due to it's large size courser is pretty easy to hit with ranged weapons as well, whereas arabian doesn't get hit as often (I assume it has smaller hitboxes... And if it doesnt it still looks smaller).
A lancer with courser can be and is deadly but I would be way more concerned about the ones who ride arabian because they kick your arse in cav duels and eat infantry as breakfast... I like the fact that there is different kind of horses to fit one's playstyle. They all have different things that people prefer.
And if you claim courser is OP, why not buy one yourself, stop whining and start winning?
You mention getting one hit due to speed bonus, the same thing applies to a destriter. My +3 has been one shotted by bows plenty of times and its not so much the speed bonus its getting shot in the head with a powerful weapon. And looking at the stat differences, i would assume that a destriter can take one more arrow or so than a courser can, not enough to make up for the gross speed and moderate cost differences.
A courser is not large, it is the same size as any horse except some of the super heavy horses. I peresonally havnt seen courseres getting torn up by ranged, in fact it seems when im riding with other cav (courseres) the archers almost always shoot at me instead of them despite my horse being "stronger", i assume because coursers are so fast they are very hard to hit, and ive heard archers saying that in game too. Not to menton seeing coursers being the last one on a team and it taking forever for archers to bring it down. Obviously the faster the horse is the harder it is to hit.
Arabians dont get hit as often because of their extremely high maneuverability, just like a courser doesnt get hit because of its extremely high speed. Arabians are only dangerous in a cav vs cav fight if you try to get into a turning competition with them which is a very stupid thing to do. If you dont realize that that isn't a good idea than i don't know. You have to get behind them and run them down (dont let them get an any kind of angle on you keep em straight infront of you), which as a courser you can easily do and its very difficult to escape from a horse that is twice as fast as yours when its chasing you, i know i have to avoid atleast 2-3 coursers every round of every game, they like to chase 1h cav.
Sure you can dodge a courser if they are bad but they will be right back on you in a position to lance you in a few seconds due to their ridiculous speed. If i can kill Arabians with a 65 weapon speed 82 reach morning star on a destriter it should be easy for you with a lance on a courser. I wont ride a courser because im a 1h cav so maneuverability is a bit more important and it leaves more skill for PS, and one shotting someone as 1h cav is absolutely everything for a 1h cav (which is why i use morning-star). Its hard enough to hit someone once and if you hti them and they survive its very hard or atleast dangerous to try to finish them off when they know ur gunning for them.
And Dynamike, my horse's name is not Lame Mane his name is Butt Fucker Bronco. Keep in mind everyone im trying to balance out cav and help the ground people.