If anything, I'm tempted to say horse archery is weak. How many times has it come down to your team having, say, 2 left and the enemy having 3 and one of your guys is a horse archer and you're glad to see it? "Oh good, our x5 is intact because this horse archer is going to win it for us"?
That never happens. It's always, "Oh good [in a sarcastic tone], our x5 is doomed because this horse archer is completely worthless. What's worse, it's going to take him 3 minutes to finally die. I guess I'll alt-tab out and check email."
Not that I really want to see them buffed. HA's strength is their ability to generally avoid getting killed, which might be real handy in strategus now with commanders, but "Nerf Horse Archers! They are too powerful!" is a call I can't really get behind.
Usually what happens is the horse archer loses his horse to a regular archer, and then he's just a regular archer with a lot of wasted points.