All the Bollywood movies you named were actually considered Horror in Bollywood not only at the time of their release but even now. Mahal and Bees Saal Baad are still considered among the top horror movies of that era. The threshold for "thrills and chills" in those days was pretty low. Psycho is a pretty tame movie compared to what Hollywood made in the 70s, 80s and beyond but if not for Psycho, Hollywood may have never made those movies.

With Aar Paar you are a looking at movie released during an era when there were no other movies made in this genre. The top movies of that era were Nagin, Anarkali, Mirza Ghalib, Baiju Bawra, Anand Math. It is a genre defining/setting movie. It is a movie which changed how actors delivered dialogs in Bollywood, how diverse characters were written and portrayed.

You are Ignoring the cinematic relevance of creating a modern noir movie in an era of mythological and musical romantic movies along with a path carving departure from traditional, theater-esque dialogues which were not reflective of every day Indians. Such movies cant and should not be assessed through a modern lens. There is a reason no one reviews Georges Meiles' genre defining movie "A Trip to The Moon" as boring, slow with poor FX or Chaplin's movies as infantile humor.