Regarding horses having a little bit of free will: I like the idea, however I'm not sure how this would be implemented. Even if successfully put into practise, I'm not sure how fun or effective it would be. Still, if it can be easily implemented, and if the horse's randomness isn't annoying, I support it. However, this randomness would make it so that you had less control of your mount: you couldn't swerve and turn with exactness, and evading attacks and projectiles would be more difficult. Thus, the issue of our current horses' delicateness comes into the light. If the idea of horse's free-will is implemented, I think horses should get an HP buff as well.
Even if there are no free-willed ponies implemented, I think horses should still get an HP buff and speed nerf. If we were only to add HP, horses would be very much OP, however I'd like to see a speed nerf in addition to the HP buff to balance shit out. It would also have the added benefit of bringing horses away from their current "ninja on the battlefeild" status, and more towards the heavy hitting, thundering cavalry I so desire.
Armor boost for the armored ponies, too, or at least for the warhorses. My large warhorse has left me rather unsatisfied--it is encased in chainmail, yet dies in six or seven arrow hits. I know that might seem like alot, BUT IN CPRG THAT IS NOTHING. I think people need to understand that archers in this game shoot like fucking machine guns, and they are large in number; there is no reason to conform to realism if realism does not cooincide with balance.
TL;DR: Look at the bolded statements. Those are my ideas, the rest is in support of teh bolds.