I actually think gruesomeness and cruelty, to use the terms very broadly, peaked in the 1970s/early 1980s with exploitation films such as Zombie Flesh Eaters, I Spit On Your Grave, Cannibal Holocaust, The New York Ripper, The Last House on the Left, and so forth. Some of these are of academic interest. For example, despite being lurid and disreputable, I Spit On Your Grave is often heralded by feminist academics as an empowering rape revenge story - not a reading I go along with, incidentally. Similarly, The Last House on the Left is often taken to be a metaphor about Vietnam. But all these films are nasty in the extreme. I find them repulsive rather than scary.

Yes, there are nasty films of that kind today (The Human Centipede, Terrifier 1 and 2, and so on) but they don't really interest me, and they tend to be rare outliers. Aside from these, I don't really think horror is any more gruesome or cruel than it ever has been.

I actually think horror films can be deeply moving on occasion. Jennifer Kent's (terrifying) The Babadook is a good recent-ish example.

If you're interested, here are some of my favourite horror films. I'd hand-on-heart highly recommend all these, and some of my choices will surprise you.

https://medium.com/fan-fare/my-twelve-favourite-horror-films-21bdeff0297b