generally speaking, DR/HD skill will determine how often and well your player can beat the opponent off the dribble and create a scoring opportunity - but when such opportunity arises, IS/JS/JR will come in and determine whether the ball goes in depending on the type of the shot you created.
In a lot of the cases, high DR/HD players will tend to shoot more than their low DR/HD teammate even if the teammate has a better IS/JS/JR attributes. This over-skill is especially evident when you just finished training 1on1 for two seasons but have not had a chance to train JS/IS yet.