I miss when horror movies had an adult rating. Although some films really push the boundaries between ratings like Red Sparrow, I feel in horror movies in particular they would probably be better off without the compromise.
There's still plenty of adult/R-rated horror films breh.
IT, Get Out, It Follows, You're Next, The Witch, Green Room, SAW, Autopsy of Jane Doe, Crimson Peak, Don't Breath, It Comes at Night, Cabin in the Woods, Trick R Treat, Krampus, V/H/S, The Sacrament, Let Me In/Let the Right One In, EVIL DEAD, Lords of Salem...
I could go on but those are just off the top of my head (with some light research to confirm some of the ratings.)