Oh, people did let him know and critisised him for it. His answer? That he his Indian and since Avatar is connected to his culture somehow, he knows best how things are pronounced and the fans should stfu.
I'm not kidding. I can't find the interview anymore but that is basically what he was saying. That's why I'll never watch that piece of shit movie.
Eh, that was the least of the movie's problems.
Actually, in some (or perhaps many) countries' dubs of the show the pronounciation of Avatar, Aang and Iroh is exactly the same as in the movie, here's an example for Aang from Germany (at the beginning when Katara speaks):
YT
The show takes a lot of inspiration from various Asian cultures and the pronounciation of some of the names or words in the show isn't true to those cultures, so i could definitely see where he was coming from with the changes, but on the other hand since the world of the show IS fictional, the creators don't really have to 100% adhere to them. It can go both ways really. One could say that the original dub in the language of the creators trumps everything, but if we look at something like Fullmetal Alchemist, where the main characters live in a country that has heavy European (or German, iirc) influences and the same goes for their names, those names are pronounced how japanese people would pronounce them. If an international live action movie was made of it, should the characters be named Ed and Al, or Edu and Aru, to stay true to the show? Personally, i wouldn't have minded the names in the TLA film if the rest wasn't so disappointing.
