Step 1. Buy a spear.
Step 2. Stop crying.
Heavy throwing axes are far superior to spears if you want to actually kill horses. Spears are best for standing there looking like an idiot while an HX circles around you and shoots you in the face, or rides past you and kills your buddies.
Consequently, NA has more throwers than I have ever seen in the history of cRPG, mainly to deal with cav.
If you're fine with "Mount and Throwing Axe" then by all means keep up the "stop crying" routine and be sure to repeat it in every "THROWING IS OP" thread that pops up. If coursers were taken out of the game tomorrow you'd probably see half of the throwers (or more) return to full infantry mode.
So again, the most contentious balance issues in this game comes down to cav, mainly coursers.