Inside rmmz_objects.js, the weapon sprite isn’t actually tied to the Hit Type. Game_Actor.performAction only calls performAttack() (the motion that shows the weapon) when the action is the actor’s Attack skill. Every other skill gets the “spell” motion if its Skill Type is listed under Magic Skills in the System tab, or the generic “skill” motion otherwise. I’m wondering if the physical skills you’ve seen swinging a weapon are set as an Attack Skill through a trait, or if a battle plugin is handling that part.
One thing to watch, it overwrites performAction completely, so if you’re running other battle plugins it might clash depending on load order. If you’re already using VisuStella Battle Core, you can do it in the skill’s action sequence instead with MOTION: Motion Type set to attack (or swing, thrust, missile) and Show Weapon? turned on.