* Anti-magic tactics, especially for a less magically inclined army (such as Nords or Redguards) fighting a more magically inclined army (Altmer or Dunmer).
Mages have weak armor. Weak armor translates to being killed in one shot with an arrow. Melee troops should be fighting normally while the arrow snipers specifically target the Mages.
I think you over-estimate the killing efficiency of an arrow fired from a considerable distance. For one thing, in the event of archers getting within range of the target mages, then the mage are certainly in range of said archers and in a duel the mages will win. You can go into an obvious loose formation, they can cast shield spells on themselves if they see they are about to become targets for arrows and magicka is more accurate then an arrow plus magicka can do area of effect damage.
And if you are a commander that uses mages aggressively, like I'm sure an Altmer army might, simple foresight of giving your mages simple padded tunics. At range, that simple piece of padded cloth could potentially stop a killing arrow to make it just a stinging hit. Combine it with even the most mild of Shield spells and now you can counter the helpless archers with a barrage of magick. Unlike LotR where every arrow fired = one soldier killed, in reality it does not work like that. Many would miss, either short, long or hitting the large gaps which equals more area then spread out mages bodies and the ones that do hit, many would be glancing hits with their energy spent at such a long range and would be stopped by the padded armor/shield combo or would hit a non-vital area. Once again, unlike LotR, not every arrow manages to hit someone in the neck from a million miles away so the amount of shots that actually hit a vital area like the neck/head/ect would be minimal and a small percentage of shots would pierce major organs and such. Plus an arrow to the foot or leg or arm doesn't necessarily mean you are out of the battle.
IMHO, archers are probably the least effective counter against mages if the commander takes the steps to ensure his mages are equipped or if the mages have the sense to shield themselves, which if you think about it most people would do if it meant saving themselves :shrug:
EDIT: Of course it's all relative to how far the archers are, if the mages choose to ignore them, and such. If the mages are focused elsewhere the archers could theoretically shoot all day at the mages, but once the mages retaliate I firmly believe that between an archer force and a mage force, the mages would win, mostly because the archers would turn and flee. No one wants to die.