I think that if you would use the aspect Disarmed it should be used by invoking it for effect. The baddie can't attack with his weapon unless he spends an exchange to pick it up, or something similar. Like a Block-lite, he doesn't have to roll to overcome it, but he needs to spend and action, or attack with his fists, etc. However, an enemy that came loaded for bear with loads of weapons just doesn't get that aspect and a GM may overrule that maneuver to change the aspect to something like Sore Hand or something like that...