Stat sticks are weapons carried or equipped by a character primarily or solely for the statistics they give. This happens when possessing a weapon gives bonuses to a character even if it is not used. In extreme cases, the weapon will provide these bonuses even when held by a character who cannot legally use it. If that sword gives additional MP to anyone who has it in their inventory, then why not give it to your mage? Your mage can't use the sword as a weapon, but he can certainly use the MP!