I haven't ever read an Agatha Christie! But thanks to the BBC R4extra have heard many of them.
I think they have a far harder edge than the cosy style the early tv series of both Poirot and Marple, and was well aware that life wasn't all apple pie and cream (eg her own first marriage).
Also she wrote into the 50s & 60s so aren't sure why this setting for this interpretation is a problem. But do think it seems to be another of those dramas where they are trying to impose 2020 sensibilities. I suspect the main character is a real shit!
Slightly off topic but my memory of the last Poirot in the tv series was very dark (I dont just mean the lighting!) and depressing. Does anyone know if this is true to the book?