Persuasion isn't really that great of a novel, to be honest, but it was forced down our throats when Austen gained mainstream popularity in the 1990's. I agree with you that it still feels like having Austen's companionship even though the story is uninteresting, and the same with Christie, although to your point, it's easier to ignore the Christie books we don't like while we can't afford to do so with Austen's few works.
Agatha Christie at her worst is still better than PD James on any day.
You might like Postern of Fate better if you could try appreciating the cleverness of the mystery, which is unlike any others. It's an original story and not a retelling, as some of them are. There could have been more suspicion focused on some of the innocent characters. She missed the chance to be extra clever with the solution, but the unfolding mystery is well executed.
@Christiefanforlife - she was just hitting her stride at the time of Murder at the Vicarage and about to write some real whoppers as far as juggling plots masterfully. Murder on the Orient Express is the best example of a book that could have gotten so out of control, but she handled it skillfully and without a jumbled confusion. She let the reader suggest the suspicious elements rather than elaborating on them as previously in the 1920's, and she finally stopped including every pertinent fact that wasn't relevant strictly to the solution. How else could thirteen people all have motives and deceptions without thoroughly confusing the readers?