I think that I had come across Miss Pym in the context of discussion about detective story tropes, so that I was primed for her not to save the day. I liked that it was an antidote to the "Oh, we know whodunnit but we aren't going to investigate it because the dead person deserved it/the murderer is terminally ill/it would just be too embarrassing" that really, really annoys me, in that allowing the status quo to continue wasn't presented as the best option but a weakness.