I think Disarm should not be given to Disciple for these reasons:
1. A disciple already has tools to deal with periods of melee combat through their enemy position control skills.
2. Disciple is competitive in its current implementation, and unless the class needs more utility for the 65 cap, then I do not see this extra period of reduced damage against melee classes as doing anything other than making it easier for poor disciples to beat armored targets, and making good disciples mitigate one of their counters (armored melee). If the class does need more utility for the 65 cap, I think a melee damage disabler or some sort of martial art "kick them so hard they can't walk straight/fumble with their sword" could fit.
3. The lore for this one is more dependent on what type of martial art monk you are imagining, for instance to my mind the Disciple would disable an enemy's body rather than their weapon, since the Disciple has spent his life fighting with just his body, he considers weapons to be less important than his enemy's vital points. Opinions vary, but a straight Disarm copy + paste isn't the best suited skill here lore-wise.