I play mainly horsethrower now.
It is an expensive hobby in terms of upkeep.
You have to fill a niche. I try to work as a forcemultiplier. In the first minutes of the battle I will target other cav.
Esp go head to head with charging lancers, as you get max speedbonus in those encounters. throw early enough for you to avoid the lance.
Or make sure you hit!
After that I will try to harass ranged camping in the rear and use my mobility to support melee that need help.
Speedbonus is key, dont waste ammo throwing at people riding away from you. And try to get alittle speed in the direction of you target.
If you opt for one of the higher tier horses you have an additional weapon in bumping, at the cost of speedbonus and manovre. You then stun them just before the bump, so that the can not swing at you.
I use 4 packs of MW throwingspears. Have 7PT, 150 wpf in throwing and rest in polearm. I can use and pickup Throwinglances if I see them.
At some point you do not have any ammo left. You can pickup ammo as you go, but it is painstaking work (for me atleast).
I tend to pick up a random meleeweapon and go 1h/2h/pole cav.
Compared to HX with all it perks horsethrowing is abit silly. But the ability to throw again faster than a crossbow is key.
Use this to circle enemies and serialbump while throwing at them constantly.
Avoid prolonged fights with other horserange. You are much more effective to your team doing other tasks.
Be opertunistic.
Good luck!
/rambling