Rewatched the movie. In hindsight, the first classroom scene basically establishes the drama and horror of the movie
...It's more tragic because if all is inevitable, then that means the characters have no hope. They never had hope because they are all like...hopeless. They are like pawns on this horrible hopelss machine."
In many ways, the movie follows the structure of a more traditional supernatural horror movie - occult forces, possession, demonic evil - but where another family in another movie would eventually find a way to understand and defeat evil, Hereditary laughs at such notions. The tragedy and horror of the film is that this family is completely hopeless, doomed from the start, from before the start. The only thing they can do is suffer, be emotionally and psychologically manipulated with no hope or ability to fight back. The drama becomes horrifying when it's all engineered, all deliberate manipulation forced upon them.
The stranglehold is so tight and unrelenting that they're subconsciously trying to escape its grip (not bringing the Epipen, the mother trying to kill the son in her sleep, etc) but they can't. That existential doom almost feels Lovecraftian, in the sense of being trapped by something so beyond their comprehension, pawns for forces that they can't fight or even grasp, and peeking behind that veil, trying to understand and fight back, just leads to madness and despair.