Yea most of those you listed would be considered classics. Compared to other genres their aren't that many great horror films. I'm not sure why the horror genre is so hard to do right but it is. I would also add this as a sort of iconic horror film.
I don't think that's true at all, but it's a genre where the same handful of films get recycled in the public consciousness and so people don't generally know of a significant amount of other great horror films, many by well respected directors from outside of the genre. I mean how many people have seen A Picnic a Hanging Rock or The Last Wave, two films by Peter Weir, who is better known for Witness, Dead Poets Society, The Truman Show, and Master and Commander? Carl Theodore Dreyer, one of the most well respected directors of all time also did a horror film called Vampyr as well as a dark drama about witchcraft with supernatural tones called Day of Wrath. Murnau directed Nosferatu then went on to Sunrise and City Girl and then decades later Herzog does his Nosferatu. Robert Mulligan directed To Kill a Mockingbird and Sumer of '42, then years later went on to direct a creepy horror film in The Other. People know of Rosemary's Baby, but how many have seen the Tenant or even Repulsion both by Polanski. Bergman did Hour of the Wolf, People at least know about the original Nosferatu (though a lot of them haven't seen it), but again these are well crafted horror films by well known and respected directors that never get mentioned, never mind those by lesser known directors. A lot of black and white films post 1960 that most horror fans know about are also absent from these general lists, including The Haunting, The Innocents, Onibaba, Black Sunday, Carnival of Souls, etc. I mean how many people have even heard of amazing directors like Kiyoshi Kurosawa or Michele Soavi or art house horror films like The Iron Rose or Possession or Habit? All of these are high quality great horror films, but you have to actually search for them.
Horror in its' effect is also quite subjective (though a lot of "lower" grade" horror films are sill entertaining), it's not as specific as comedy, but it's still a very reactionary genre in terms of immersion and overall mental effect. Good horror need not have all the same elements as good drama, as a lot of times the offbeat nature that comes with the lower budget and more amateur conditions adds to the effect.
Horror is a genre that's easy to get into on the film making side and seems easy to create given how many low budget films turned out to be classics, but is often difficult to take hold. The 80's had its' glut of horror films, but most of them were fun even if they weren't classics. The digital age though brought on a slew of horror films with a lot just not working at all. People want to be famous and get a quick buck now more than ever, and social media is all the proof of that, so you see these people that seek attention and have deluded themselves into thinking they have talent making films. Compound that with the ease of making films in the digital age whereas before you needed people that would know how to handle film including color timing it in post production, needed lighting people and color gels, film specific editors, analog audio people, etc. You needed training/schooling and studying to be able to do a lot of things that can be done with digital cameras and software much easier, so you had to put a lot more time into the craft of film making, and that sort of thing weeded out a lot of the hacks that today can get crap onto Netflix and onto dvd.