It is clear that the Sword has been given to Harry to do as he wishes, and the Sword in the Stone myth does actually reinforce the “powered by an Angel” theory Harry has been putting forth. The angel decides whether someone is worthy or not.
It would certainly rub salt into Marcone’s wounds about losing Camelot, as well as rub Langtrey’s face in it that he is living in the real Merlin’s castle, with Excalibur just like the real Merlin.