Hard disagree about horror films and 'scary movies' needing to be 'scary'. That's an extremely subjective measure that just starts useless arguments.
Just like any other film, what it actually needs is good writing, good acting, and good cinematography, parts which are more concrete than whether something's scary. The horror part is essentially just an aesthetic which a movie can sit within.
Also, quite often the view that 'scary movies should be scary' just leads to directors creating films that are hard to watch, period - full of vapid jumpscares, scenes made to just gross out the audience, and often just torture fetish content. It's a terrible metric to aspire to that generally degrades the entire genre imo.