So what I'm getting is that she ra is basically the avatar.. whose job to bring balance and harmony to the world but they need to let go of earthly attachments to reach their ultimate power..
the horde and hordak are the fire nation and the fire lord who will destroy the world to get power.. also i think that makes catra zuko who needs to find their own destiny..
the princesses and their kingdom are essentially the elemental nations that needs to unit and be in harmony
and mara is basically korra who broke the connection to the previous avatars.. hmm interesting..