In the case of the A-4 it was the strong adverse yaw reaction to aileron input that made the aileron the dominant spin recovery (as well as spin INDUCING) control. It was unlikely that you would ever get an A-4 to spin using rudder input only. OTOH, a bit of aileron at the top of a near-vertical 0-airspeed maneuver was almost sure to put you into a spin instead of a falling leaf...
FWIW, the full roll rate of the A-4 could not be achieved with aileron alone; significant rudder into the roll was needed as well.