On Celestia: interesting takes; I have never seen Celestia in danger of running out of magic in a fight before, and also how her low magic is indicated by her mane reverting back to normal.
On Luna/Nightmare Moon: I have seen one version of Luna/Nightmare Moon who was…damaged by their exile on the moon, but the first one was still mostly sane, just more of a traumatized death-seeker and a vengeful warrior princess than a would-be conqueror. This one, however, was actually more or less broken by her experience.