Horse throwing can do amazing amount of damage. Ask zlisch how many survives a charge+lance in the chest. The reason you don't see many of them is that both HA and HC is much more accurate while carrying a lot more ammo.
I'll answer with how many dies instead, 50-60% of all light armored people (horsecrossbowmen, light infantry, my old friendchers, ha, etc), and people who are already wounded, this is when I'm riding towards them and they're standing still, around the same amount who'll survive me shooting them with an arb with the horseranged damage penalty if we're both standing still. also Gurnisson, it's funny how you talk about your arabian never surviving any ranged hits yet ride around with two throwing lances in your horse, thrown while you were riding towards me.
Only really decent suggestion to fix HX is forcing them to only reload while trotting, that should give other cav some minor chance of catching them, it'll mostly just be like kiting archers though, if you slow them down, and they're still the least faster than regular cavalry, then they'll just run for longer before shooting, it's still one of the only suggestions that won't have extremely retarded consequences though.