It’s interesting…but I thought the movie explained that weird Barbie’s behaviors
and mannerisms came from being played with to much, I thought that did add to her back story quite a bit.

The splits-if you play with a Barbie enough her legs lose their friction on the hips and they constantly are just lose-thus constantly doing the splits. I have a couple dolls that did this and their constantly doing the splits.

Haircut-I’ve seen this so many times, a little girls eventually gives her doll her own haircut. So her hair cut was done by a child.

Makeup-they show a child actually drawing make up on her with a crayon.

Wisdom-weird Barbie knew all about the ins and out of Barbie land because she has been around longer than the other Barbie’s. She is older and wiser, has knowledge from being played with.

Isolation-I may be making a leap here, but I thought she lives alone on a hills because that is where the old Barbie land was, and the newer younger Barbie’s moved into the lower lands. To me this was hinted at in the opening when the girls playing with baby dolls were in a hilly mountainous area.

I do see your point though, she plays the roll of the knowledgeable outcast, a common trope found in movies such as the magical black person or the manic pixie dream girl, etc. I do feel such characters are coded as queer or autistic.-and are often under developed.
That is a trope that nods at us and mis represents us. Often the magical autistic or queer person living in isolation and being feared for being different appears-like Elsa.

However I would argue her character as a Barbie that has been overplayed with and thus has various qualities shows more character development than usual in usual such tropes.