@Applelight Limited
Well, If they were created by grogar, as is the current popular theory, that would explain their confusion at flurries natural birth.Also, it would explain nightmare moon and the potential within celestia to become daybreaker. Grogar probably created the sisters to be weapons and their evil forms are what Grogar intended them to be.
@MasterNexus
Twilight is not the only pony that celestia has to think of. Twilight has earned the right to rule and Celestia has given her the legitimacy and executive power to do so. But Twilight is not immortal and neither are her Friends. The medallion ensures that whoever is in charge when they are gone is not sole owner of the sun and moon.She’s handing the reigns of power to her people rather than bestowing it on just one person. This is the exact kind of move that I would expect the Princesses to make if they are retiring. After a millinia of buildings and guiding equestrian society, it’s time to see if it can stand on it’s own.And if in a few generations time, their people need them or the medalion is abused or destroyed, The princesses can step up again and course correct. They still have their powers after all.
Their importance is in no way diminished by the creation of this medallion.