Moiraine enters the Tower life proper, Moiraine exits the Tower life proper. The Cairhienin succession provides a believable reason for her to scoot. Threats to the character’s identity always work best to me. In real life, unhappy people often seem to have threats to their identity, their destiny not conforming to their wishes. And since we want Moiraine to be happy, we want her to not be queen.
Knowing the rules of who you defer to and why, it is obvious that for most Aes Sedai, the path to power and prestige is to be a Sitter. The scuffles for those three seats must be epic. Those who lose, join the Black Ajah? Maybe settle for a decent rank in the Ajah as eyes and ears or Eighth Reasoner? Or just conclude that you should set out into the world where everyone defers to you and leave this political claptrap behind.
The introduction of so many more Aes Sedai by name nicely creates the impression of the numbers of Aes Sedai in the Tower and the complexity of their relationships. I’m not sure the same could have been done without introducing so many of them. Of course, there is a benefit to having half of the new introductees already known by readers in the main series, giving them tags for the readers to identify them and keep them apart in their minds.
Having only Elaida to base our perceptions of Reds on, we get Sierin, who should have been Red. Yikes. Stereotype reinforced.
Moiraine and Siuan are living each other’s expected lives, Siuan in the Tower administrating, Moiraine on the road living adventure.
Providing motivation to a character is easily done by attacking their perception of their identity.