If you can protect your archers long enough that they run out of ammunition, you have made the most of their role on the battlefield. But that is usually only possible when the opponent is attacking, such as in a bridge or hill defense. That is why I like good horse archers - the Mamluks and Byzantines have a big advantage in that respect, since they can shoot and fight equally well.

Try this tactic - always have at least on unit of arbalesters in your army and have them always shooting at the enemy general. Could turn the tide of battle