I think obsession does a better job at underlying themes.
Okay I know this is a really hot take considering all the hype and everything (I know the movie came out in 2018 while Obsession came out in 2026), I did just finish watching the movie today so I might just still be processing things. All the spiritual stuff in the movie feels as if it was an afterthought during production of the movie and doesn't really tie back into how the themes of grief, guilt, and neglect affect a family as a whole.
My main problem with it is how unnecessary and "extra" it felt, I'm not saying it's a bad movie, but it did kind of feel like it was relying on shock value a bit to keep the viewer engaged. I think if they kept going without the spiritual stuff then it could've been a lot greater. There were a lot of times where people wanting something to blame was shown but not addressed, like Annie wanting to blame someone and Peter was right there but never actually got to the point. Same with how people cope with grief as a whole, it kind of just abruptly stops almost halfway through the movie and instead focuses on the paranormal and godly figures all the sudden? The main thing I got from the trailers and teasers was that the movie was going to be about grief.
Some mild spoilers ahead for Obsession if you haven't watched it.
Obsession on the other hand gets straight to the point in the parallels in how obsession can actually ruin a lot of lives and harms a lot more than good. It was straight forward and showed how toxic relationships are almost co-dependant in a way where neither is benefiting at all. It ends up turning into a clusterfuck that no one is able to repair because of how far gone the relationship has gotten. The one wish willow and how it ties into the story is more straight forward and helps transition into the rest of the story rather than being an after thought.
All and all though, this is just my opinion. I feel as if Hereditary could've been better but it's still a good yet thought provoking scare for those that want something new. Thanks for reading and hope y'all have a good day.
Edit: It seems that I somehow missed the whole point of the movie, I'm just gonna sit here with my dunce cap on. Sorry for wasting y'all's time.