I found it quite entertaining. I had listened to about 2/3 but it was coming due at the library, so last night I found the text online and read the rest. (A great advantage to reading old books.)
In fact there is one character in the story who recognizes Miss Halcombe's superiority: the sinister Count Fosco, who assists the heiress' evil husband in getting rid of her and stealing her money. The Count so much admires Miss Halcombe's intelligence and courage that he falls in love with her despite his black heart and alters the sinister plot to insure she will not be harmed, which may have been the conspirators' undoing. I kept thinking that if Hartwright was too foolish to recognize her virtues Miss Halcombe should have run off with the Count to pursue sinister adventures across the globe.
The other thing that struck me was that rich Victorians were very worried about loneliness. There is a constant effort to provide people with "companions," so pervasive that people with class and education but no money can survive their whole lives as companions to various rich people. Miss Fairley is provided with a whole series. Her husband brings Count Fosco into their house partly to assist with sinister plotting but also to have someone to talk to. It seems assumed that poor people, who must live in crowded tenements or villages, have plenty of companionship, but even respectable middle-class families often seem isolated and desperate for company.
So it is perhaps the spread of wealth and respectability that contributes to our problems with loneliness? And should be bring back the professional companion?