That's an oversimplification. Skilled archers, especially in numbers, are a force to be reckoned with. For example:
https://en.wikipedia.org/wiki/Battle_of_Agincourt
Or think of horse archers. The mongols used them to great effect, and the Romans lost 7 legions against them, despite their testudo supposedly being next to invincible against projectiles
Volleys do have their place, but mostly as a way to open the battle, and at long range. You are correct that that can often be used to provide breathing room for troop movement. However, once the fighting starts, archers usually start picking individual targets and fire at will