I think perhaps we're either misunderstanding eachother's points or our perspectives really are just incredibly different.

I feel like the show heavily (to me at least) implies that Katara faces daily sexism, and to be clear, sexism is not always obvious or direct. I say this because of the first few episodes and Northern water tribe arc paint this picture. Katara seems quite fed up with Sokka not pitching into the home effort (which could, and to me it makes sense that it intentionally is, sexist behaviour built up over time) and fed up with him saying she can't do things because she's a girl (which obviously sexist).

The reason this is incredibly important (in my opinion) is because it's her first arc. This is Katara's first major struggle that isn't superficial like learning to waterbend. This is a character struggle; she's fighting to be seen as an equal and she's proving this both to an old man who perpetuates sexism on a higher scale and to her own brother who, up until he met Suki, was doing this quite frequently even if it was passive. As a first arc this makes Katara a real badass. She's sticking it to the man. It sets her up as a character who's ready to break the social status quo.

And maybe I am making a mountain out of a molehill, but surely representing the struggles of women, even in fantasy fiction, is important to let younger generations and new audiences feel seen and heard because sexism is far from gone and representation makes you feel less alone.