The beauty about Avatar was that it wasn't a neverending series like most shows but a story that had a finite span. The downside of that is that a high level of efficiency is required in what ends up on screen. So a show like Smallville would have got away with an episode like The Runaway but Avatar not so much.

Audience interpretation is the most valid assessment of a story. It's no good Rowling telling us Harry is a hero if fans have a problem with his use of an Unforgivable. The same with Mai. Of course there's total bias which is easy to spot. But when canon supports a perspective then it should be acknowledged. And actually, it's the "boyfriend >>> brother" reading that is the most direct reading. A deeper, more meaningful reading is precisely that - a deeper one, based a lot on our biased speculation. Which is why though I enjoy her character, I can't dismiss criticsm of Mai.

Is that a problem for where she is at the end of the story? No, it's not. But a good story isn't just about the destination, it's also about the journey.