Generally immune is a weak design and should be used only for unique bosses.
About disarm and whips – it would be better to make chance to disarm depend on target’s melee/ranged skill. And also distance between targets should give penalty to hit. On the other hand cause all this moments decrease value from whips I think in case of hiting target but not disarming some debuff could be added on tarhet – like -10 melee/ranged skill.
