I'm not so sure about Aladdin being a magi of the old world in the same regard as the other three are of this world. He's from there, but he sure was late to the party if he was born right when the world ended (and Solomon was presumably made a King by his own magi). In fact, could magi be an entity that only exists in this special world Solomon created? I can't remember whether they said magi existed throughout the ages or the worlds.

Or was Aladdin Solomon's magi whom Solomon "preserved" somehow? We only know that Ugo was Solomon's Djinn - and if Djinn are acquired in dungeons then I assume a magi was around in that world to erect them.

As for Scheherazade dying and Aladdin replacing her, I've found it weird that not all of the magi appeared at the same time. Are they supposed to be staggered such that each generation is supposed to try correct errors of the past magi by choosing a more appropriate king if required? We've been told that the magi choose their own king, but it needs not be a competition like it sounds like.