It must be noted that Hasboro threw the premise at the writers completely out of the left field with no prompting. It was basically: "Do a Wedding for the season finale. With Princesses. Girls love Princesses. K thnx bye!"
Cadence, Princess. Foal sitter of Twilight who is now also a Princess. Twilight now being a Princess, Shining armour by textbook royalty definition is now a prince. Shining, marries Princess Cadence thus as there isn't one currently in Equestria, promotes both Cadence and Shining to King and Queen. Therefore giving them higher power in rank than Celestia an Luna.