The Ancient Dead require completely different tactics to fighting bandits, orcs, and goblins. While Ancient Legionnaires function very much like Orc Warriors, the armor requirement to effectively fight them is not nearly as high because their swords are basically weaker Arming Swords (that don’t cause bleed, unlike basically all bladed Orc weapons). Other thing is that Legionnaire shields are reasonably breakable for Axe specialists, unlike Warrior shields which are a waste of time to try to break.
Yes, Archers are a lot less effective against the Ancient Dead, but they are not entirely useless when the Legionnaires come around; they still do full damage to armor, so they can still armor-strip the Pikemen. Which make them really easy to get chopped by a Greatsword or Warbrand user (via Split). Also, since the Legionnaires have really low initiative, it’s really easy to stack Overwhelm on them with your Archers. Heck, even full plate users can stack Overwhelm on them.