In defense of Aang and Katara : all the nations in ATLA are obviously based on Asian cultures.

The Fire Nation is Imperial Japan, with some touches of Chinese influence for clothes and architecture.
The Water Tribe are Inuits, as evidenced by their life on the ice and their fur clothing.
The Air Nomads are Buddhist monks with Tibetan clothes and rituals (like using toys to find the Avatar, very similar to how they find reincarnations of the Dalai Lama).
And the Earth Kingdom draws heavy influence from China, but from a lot of different aspects, like Ba Sing Se being a big reference to the Forbidden City, or their government being a police state with heavy propaganda like in the Ming dynasty. The Dai Li is also named after the leader of a powerful secret police of China during the 20th century.

TL;DR : yes, Katara was whitewashed. Aang… not really.

I get the majority of it, but I dunno what pointing out that Jesus is Jewish is supposed to mean. He lived in the Middle East, He likely would have looked closer to something like this: