Finally watched 1963's The Haunting. A capable, if overly literal, adaptation of a great novel. The TV show explores the themes far more thoroughly, despite not depicting the same events at all. Also, scholarly sources seem to agree that the movie makes Theodora's lesbianism explicit, but it absolutely does not, except in an alleged deleted scene where she has a bad breakup before coming to Hill House.
It's very strange to watch a massively influential movie after seeing all the shit it influenced. I seen Ti West and Mike Flanagan movies, so I basically already saw this one, by way of cinematic Telephone.