I'd be prepared to give Bumi and Kya a second chance. They both need some work, sure, and were both frustratingly passive in Book Two, but I still feel there's a story to be told with each. I presume that Bumi didn't get to be a Commander for nothing. He must therefore have some steel. I'd love to see him in action - dropping his fool's façade. I know that's a pretty big part of his nature, but he must know when it's appropriate and when it's not. I want to see an event that pushes firmly into the latter category. Kya likewise, needs a story that lets her show her talents, that shows the person who became a Master. After all, talent is nothing without application. I want to see something more than healing on demand when someone else's adventure calls for it and she just happens to be there as a third wheel. Ultimately, I think the key is to split them up. Together they are all prone to regressing back through the years and behaving as if they were children - even Tenzin. Split them up, give each some genuine responsibility, and there would be no other option than to show the audience why Bumi was a Commander in the Second Fleet - why he found himself in situations from which, in retirement, he can spin those elabourate tales - why he was trusted with people's lives, and why Kya is a not only a waterbender and healer, but a Master. Up to now we've only been told they are these things.