In The Last Airbender and The Legend of Korra, we saw some disagreements between Avatars and world leaders, but it was never clear to me who should have the last word (of course, not talking about wartime, so Aang vs. Ozai is pretty obvious.)
For example, when Avatar Roku discovered that Firelord Sozin had started the war, he confronted and attacked him. Still, when Korra visits the Earth Queen, I would have expected that Korra's command for the queen to hand over the air nomads must happen, but the Earth Queen did not acknowledge Korra's authority over her.
Any other references on who is actually superior to who, maybe from comic books, the chronicle books of Kyoshi and Yangchen, or some other source?