Non comparable things.
Horror movie is entire package of visuals, suspension, certain pace, when to strike at exact moment to scare you or make you feel scared throughout the movie like something's gonna happen anytime. And then entire package of sounds from movie soundtrack to audio effects and dialogue.
All horrorcore rap can offer is some shock value storyline on a beat
Watch a classic movie like John Carpenter's The Thing. The location they picked up, the moment when they know they fukked up and got stuck in that base. And all the time the movie makes you involved in it, analyzing every character and wonder what happened that you did not see, who actually is infected already, will they actually survive, and the sickening visuals which look impressive even up to this day.