The Fanalis tribe's lack of ability when it comes to wielding magic makes sense with The Reveal that they are actually a non-human race of beast-men that were somehow granted human-like forms. The flashbacks of Alma Torran show that magic was a power granted only to humans to give them a much needed edge over the other more physically powerful races. The Fanalis tribe can barely use magic because they are barely human.
The key to the identity of the Magi who betrayed Solomon was laid in the first two flashbacks we had of Alma Torran. The individuals who were having those flashbacks were Ithnan and Gyokuen, both members of Al-Thamen and enemies of Solomon. The Magi who was shadowed in black in the flashbacks? Sheba who was the most loyal to Solomon. Since Arba was the other female Magi, that left Arba as the only one who could be Gyokuen. The flashbacks fooled everyone, because we did not take into consideration how the ones who had those flashbacks were all members of Al-Thamen, so of course the one who remained loyal to Solomon would be the one in shadow - they saw Sheba as the enemy and themselves as "just".
Aladdin is a peculiarity because he's the first fourth Magi since the beginning of times. The reason of this is Aladdin is the son of one of the first Magi and Solomon, who created the white Rukh by becoming the white Rukh itself. The Rukh's support and protection is Solomon's way of taking care and loving his son.
Genius Bonus: The language of "Torran" is Cuneiform, one of the oldest writing systems and was the main system used by Sumeria.
Ja'far is appalled at Sinbad for trying to recruit children (specifically Aladdin, who is 10 years old at this point) to help him defeat the Fog Troupe. At the time, it seems like just another instance of Ja'far playing the Straight Man to Sinbad. Then, much, much later, you find out that when Ja'far was 10, he was a hardened child combatant in a fiercely, intensively abusive military subdivision of assassins.
What, exactly, must have been done to Ja'far starting in his very early childhood in order to turn him into the character he's introduced as in Sinbad's Adventures at the Improbable Age of just 10 years old.
Judar's a Magi who himself has "fallen into depravity", and we know thanks to Aladdin's dose of Solomon's Wisdom on Judar that he was kidnapped and seized by Al-Thamen at birth; now start to think about all the horrible, horrible things Al-Thamen must had done to Judar that broke him enough to curse his fate and become the Psychopathic Manchild he is today.
It's later revealed that Al-Thamen manipulated the chemicals in his mind with Black Rukh, forcefully causing him to fall into depravity.