The durability of the player characters isn't really the big issue for me when it comes to trying to do something more horror-related with 5e (or D20).
Here I go simping for Savage Worlds again...
Character power is overstated as a problem when it comes to horror for a couple of reasons.
First, people have the idea that in horror games (especially Lovecraft) the PCs should end the game dead, insane, or both. This is not true. In most horror fiction (including a lot of Lovecraft) the characters "win", survive, or achieve some victory even if it minor.
Second, Savage Worlds works well for horror despite stacking the deck heavily in the players favour. I think the reason for this is that enemies are always a threat. A zombie in Savage Worlds can get lucky with exploding dice and ruin a PCs day. In contrast, a single zombie in DnD can't kill a PC unless it spends several turns attacking.
It's not that the PCs are powerful or durable, it's that the rules can result in monsters that are zero threat.
Third, DnD has magic. Spoony's video on Cthulhu-Punk is a great example. No one players GURPs Cyberpunk, only ShadowRun, but the magic in ShadowRun renders the supernatural elements of Cthulhu-Punk moot. Part of the reason I'm hesitant to run Ravenloft for people is because everybody knows it already.
All of these things can be fixed with fudging and houserules, but like you said, just play something else at that point.