Archery is expected to be harassment rather than destruction of the enemy, and is most effective against poorly protected targets or where multiple shooting units can target the same unit, which is easiest to achieve on the flanks, or where terrain allows the stacking of units, such as bow units on a hill behind other shooters. Normally you would be aiming to either clear skirmishers or cause discouragement in the turn in which a combat will occur. Is is indeed quite difficult to achieve this against outliers like D2 units or D4 or better in phalanx or shieldwall. A more typical D5 or D6 target is a different proposition. Overall, it is difficult to win with a force totally reliant on archery unless the enemy obligingly remains static.
"No one ever achieved anything without making a few mistakes along the way"