That kind of argument is against a Jane Austen that never existed. She never was a saint, that's a misconception. She was intelligent,and had an unusual talent for writing, but otherwise was not much different from you and me.

So Jane Austen is not writing about servants or other members of the working class. Why should she? First of all I can't see how they would fit into the kind of novels she wrote.
Can you believe that any publisher would have accepted a work including a lot about the living conditions of farm labourers or servants?
Who would want to read it? I don't think she ever got the idea.

I'm convinced that with her perception she was critical to a lot of things in her time, but not publicly. Remember womens situation in general and her situation in particular.
Dependant on her family, and a family with conservative values and
associated with other families who shared them. To what degree She shared those values we'll never know. But she certainly didn't want to rock the boat. That would have gone against her own family and friends.

She is writing about her own class. Does that mean that she didn't care about any other people?
Of course not. I'm sure she did, I think we can see that in many comments she does in her letters, and we can see it in the novels.
Her religion might have played a role in this too, perhaps leaving the questions of justice to God.

If she had lived for another 30 years, we might have seen her writing a different kind of novel. She would naturally have been influenced by the changing times too.

Leif G-n