This is ... kinda true.
It certainly doesn't work for "Slasher Horror" after 5th level, but that's a fundamental misunderstanding of what a slasher -is-, in the end. Sort of the same with Creature Feature horror after level 2-3. Fighting "One Vampire" is either devastatingly implausible when you're too low level, a single combat encounter when you're near the right level, and a speedbump thereafter. Because if you're dealing with a monster, or a singular human or whatever then it's just another combat encounter.
But horror isn't in the monsters or the dice rolls or the amount of HP you have left. It's in the narrative and the delivery.
You -can- tell a good horror story in D&D... It just requires buy-in from the players and the knowledge that combat is going to largely step on the atmospheric and narrative elements of horror as people roll nat 1s and play it as comedic or get frustrated by them.