The Reverend Mr Brocklehurst is a snob, a hypocrite and a sadist but his influence at Lowood is mitigated by his rarely bothering to put in an appearance. The greatest evil of his regime is starving the school of funds (though perhaps he is a just steward and the funds simply aren't there). The head mistress or Superintendent is humane and conscientious and the staff she's saddled with are mostly decent but, like the children, overworked and underfed. One of them is a little too fond of picking on kids she doesn't like. The food may be lousy but the education provided seems- by the standards of the time- to be more than adequate- as may be judged by the accomplishments Jane emerges with. Bronte isn't a crusader. She's not saying- as Dickens would have done- "We must wipe institutions like this off the face of the earth." Rather she's telling us how things are. These places exist; they perform a necessary function; they're run by people who are variously gifted and motivated; it would be nice if they were better funded. I think this makes her a realist.
Jane is happiest during the typhus epidemic. Discipline breaks down and she and her mates get to roam the countryside at will. Without labouring the point, Bronte is clear-eyed about the heartlessness and resilience of children. It's not exactly Lord of the Flies, but it's getting there.
Helen Burns is one of the first of the Victorian martyr children- and one of the most plausible. Think what a horror Dickens would have made of her. Bronte is good at dreamy spiritual people because she was one herself. Dickens wasn't because he wasn't.
The real Mr Brocklehurst sued Bronte for defamation of character- thereby making sure that nobody would ever have any doubt who she had in mind. Twit!