You can't balance mechanics with effectivity.
Horse archers being not only invulnerable but also unavoidable for a lot of classes in a lot of scenarios is definitely a mechanics problem, especially since those classes at a disadvntage are supposed to kill every enemy, inlcuding the HA.
Lowering accuracy, damage, shot speed or other values is changing the effectivity. Which doesn't effect the mechanics mentioned above. Not at all. All the devs were doing was tweaking the attractivity of a class, lowering their effectivity to a certain level where the mechanics problem doesn't really kick in any more. Might work, but only badly, and is a terrible decision design-wise, concerning "fun" in the game. And fun is what games are about. The current solution still has less fun for the HA victims, because the same annoying mechanics are still working, like getting kited, but on the other hand the fun for the HAs is lowered as well, like having a crappy lethality.
The devs would need to either limit the mechanics of a HA (which isn't possible, I think. He MUST be riding, and he MUST be shooting from horseback while moving), or to improve the mechanics of infantry vs. HAs. Which is not impossible, but incredibly difficult. As some of you may already have expected, I again refer to the only solution I found for the problem: battle mode turns to conquest mode.
I saw a lot of wrong arguments here (use brain/teamplay to fight HAs? And how much brain and teamplay do HAs need?), but except for that one in the brackets I refrain from answering them, as there is no point in doing so and I don't want to make the post even longer.
Yes, the HA skill is UP. No, it should not be buffed again, it wouldn't solve the general problem at all. You will have to wait and see what the WSE2 will bring, but unless the devs change something in the mechanics area, your lousy deadlyness has to stay Cris, as the "least terrible" solution we have atm.