In Speed Dating for Ghosts, Spooky Peter teaches the player on how to properly haunt people, and his most important lesson boils down to "the goal is to become a presence, not a nuissance". I think more about that than I probably should.
Anyway, this superbly applies to any form of combat in horror games. If your enemies are to weak, they start to feel like padding in-between the juicy parts: "ugh, more chaff to shred before I continue". Conversely, if they are to strong ... well, after the third time of dying the same way in the same place, it's not really scary anymore, but just frustrating. And there is only so much adjusting of the game's difficulty you can do to hit the goldilocks zone for every player regardless of their skill level.
That's why single, "Hunter-type" enemies imho work better, usually. Mister X, the SA-X, the Xenomorph, even the Pursuer from Dark Souls 2 They each have an, err, "Aura" of fear, terror and anxiety they project, which common enemies just can't.