Oooo! Aye, that makes sense about Belgemine

Yojimbo, Anima and the Magus Sisters are noticeably stronger than the other Aeons (with the exception of Bahamut, perhaps) so since Anima is a "failed Final Aeon" maybe the other two are failedd FA's as well. It would explain the name "stolen Fayth" for Yojimbo: stolen from Yunalesca's dome and it would explain Belgemine's proximity to the Magus Sisters.

PS: Duality you have a point, but I prefer to think evil Bevelle Maesters care not for Spira's people, they do what they do only for power.