HA have always pretty much been anti-cavalry. They are very good at this role. When it comes time for needing to take out ground troops, or to melee when dismounted, they are like fish out of water. Very specialized, niche class, but coming from someone who's always on a horse, they are crucial to keeping me away from their infantry (well before the nerf patch anyways). I generally try to avoid HA's, so they can "keep me away" from certain areas of the map (to a certain extent, it obviously all depends on terrain and the map).
HA's working together with their own friendly cavalry lancers/1h's are good combo's for taking out enemy horses.