I think you missed the point of 12 kingdoms... 12 Kingdoms is a world where "divine decision" surpasses all silly mortal social conceptions.
Regardless of whether the chosen king is a begger, a pirate from Japan, or a highschool girl, if the "will of the heaven" decides he/she is a king, so it will be. And in the next phase of the story, even if you are a princess, or a farmer's daughter, once the King decides so, the two will be treated the same.
Magi is equally fantastical, down to the foundation of how the world was formed.
The entire point of Magi (and djinns) choosing candidates for the "king of the world" instead of human society and its monarchy is, that in front of the divine and godly, the mortal human society is nothing but a fleeting, mundane concept. If you say you read spoilers, you might wanna check out Sindbad's story. Actually, it's anime related, since Sindbad's gaiden will
exclusively be part of the DVD/BD releases of Magi anime.
/shamelessplugforDVDbuybuybuy