I think the issue with that is (and this is probably the same issue that DC is currently having right now with all of their legacy characters) that non-whites seem to have a much easier time relating to white characters than vice versa. This is probably because the white race is seen as the "generic" race, so there wouldn't be any issues with ethnicity or culture, as most white heroes aren't typically portrayed as anything other than WASPs.
I believe the problem is that is the perception. I also agree that white is seen as generic. If I were to describe a character and leave out race, most people would assume the character was white.
I personally believe it's a problem that requires an active solution, not a passive one.
I never watched Last Airbender, so I barely know anything about about it, but I will say this, Last Airbender ISN'T iconic like Spider-man. Like I said before Spider-man is one of the most recognizable fictional characters in media today. Last Airbender doesn't even compare.
Spider-Man is. Peter Parker is not. There's a reason Spider-Man has been adapted into other cultures. Peter Parker on the other hand, does not survive the change. I'm not going to post the pictures again, I've been over this.
People need to stop bringing up Black Panther. Seriously. It's fucking up your whole argument.
I know! And the best part is they don't know why.
I mean black panther is a scientist who and a king of a secret technologically advance nation who's symbol/title is that of a black cat, you could make that about a white guy too.
Lemme explain why. Using story.
Black Panther is the story of a son taking on his his father's mantle, coming fully into leading his people and his culture. Black Panther is the apex of his entire sociological group.
Change his race and you have to change his culture as well, otherwise what you have is a Last Samurai-esque story. Different plot completely. Definitely doable, but completely different story.
Captain America is another. Changing Captain America's race means changing his origin, since his original intent was as a propaganda piece during World War II.
Changing Spider-Man race? No change. The story remains the same.
And of course Steel is a black Iron Man. As much as Apollo is a gay Superman. Yes, you could change Steel's race without any issue.