Archer-centered armies existed in the past, but that's 3000-4000 years ago. Improvements in shields and armor rendered them far less effective, and a spear or sword in combination with a shield became the standard for the next 2000+ years, until firearms became reasonably effective. During MOST of the Middle Ages, archery was a fairly effective supporting arm, not the primary force of an army.
Cavalry was potentially overwhelming in Warband because the archers would shoot at where the riders were at the moment, not where they would be when the arrows arrived. An oblique course toward the archers would lead to 90% or more of the arrows flying harmlessly behind the horsemen, and then the riders would butcher the melee-deficient archers. If you stopped before contact, you got pin-cushioned. A single rider could distract most of the opposing archers, meaning that the enemy would waste its arrows instead of targeting the approaching infantry. Given the ability of an archer to lead a target with a great deal of precision, that horseman is now as good as dead. Archers SHOULD be able to lead a target, but doing so should significantly widen their target box, making occasional hits more likely than in Warband without giving them 21st Century computer-guided accuracy.
Shielded infantry was also potentially overwhelming against archers in Warband, unless the infantry was lured into facing away from the archers, or the weight of fire was sufficient to break the shields. Having the archers able to aim shots against shielded infantry with any precision in order to hit legs at a distance, or destroy shields with less arrows, seriously reduces the effectiveness of the infantry below its historical performance. Once again, the archers were there to take advantage of opportunities as they happened while the main melee forces clashed, not to utterly destroy an incoming charge by themselves.