Although a bow can't compare to a repeating crossbow, it is much faster than a standard crossbow. As for accuracy, that depends on the skill of the user. In the game, archery comes with a certain degree of assistive judgment. Simply put, the game effectively enlarges a zombie's head by a factor of two; hitting anywhere in this enlarged area counts as a headshot. If it's not a headshot, it's meaningless—you could shoot a hundred arrows and still not kill the target. That's why out of all weapons, archery is the most skill-dependent.