Hold on, in this AU Lu Ten didn't die? But then Iroh would have been made the Fire Lord, not Ozai. The only reason Ozai overtook his older brother was through manipulation following his son's death.
Fantastic point! I'm glad someone finally caught on and called that out. I won't reveal much, but I will tell you that Iroh stands to be one of my favorite characters, so I put an immense amount of effort into his rewrite. You see, without the death of Lu Ten, I had to fabricate a whole new plotline and series of events to make Ozai the Phoenix King and Iroh the Fire Lord regent instead of the Fire Lord himself.
I won't reveal too much, but rest assured that Iroh will play a very similar role in this AU as he did in the canon and he hasn't changed too much at the core. That said, fantastic observation. I came along that flaw during the original conception and I could not bare to make Iroh another power-hungry Fire Lord/Former General.
It would be fair to note that Ozai and Ursa essentially assassinated Azulon and used the cover of Iroh's failure to conquer Ba Sing Se after 600 days (due to the death of Lu Ten), so it wasn't just outright manipulation. Shit was straight deceitful. Ozai is a dick.