>>97972630I fucking love this kind of subject, so here is the thing:
Nigga, this is normal.
Take the Roman Empire for example, they let their vassal states have their own kings and leaders (like Herodes among the jews), as long as they were under the authority of the emperor in Rome, they could do as they pleased.
Omashu probably was an indenpendent state, before everything being unified by the King of Ba Sing Se, and being a major city, they probably agreed to accept his authority as long as they kept their own governament and traditions.
Similar stuff happened all the time across history.
