Avatar clearly takes place in "China-land", even using Chinese characters on signage that appears in the show (I remember the missing poster had something similar to 飛天野牛 which is literally flying bison).

The "ay" sound used to pronounce "ayng" like the original doesn't exist in Asian languages, in fact is a very rare sound to appear in pretty much any language I've found. Listen to the "a" sounds in this song for an example https://www.youtube.com/watch?v=plvSpVSdJWU

"Ong" is the culturally correct pronunciation of Aang's name and the people who cry about this are acting like children who don't know any cultures outside their own in my opinion.