I'd just like to say, it's just silly that this has to be cast into an empty slot. Steal costs the same amount as this puppy and it doesn't proceed to hurt you every turn for the rest of the game -- in fact, it takes the opponent's weapon away by giving it to you. I realize that it's Other quanta instead of typed quanta, but still -- it would be in no way OP if it did play itself over the enemy's weapon.
Also, please note that Protecting this wouldn't keep anyone from playing another weapon over it. If it did, you'd never be able to play another weapon over a Morning Glory.