Yes, art movements get accepted over time, become part of the establishment as you said and after some time become irrelevant. So then new forms of art emerge. Maybe this is how nature also operates, always seeking to make new things and innovations.
Well, I think at this point with the internet, people have become more accepting of darker things and used to many things. It’s not really the “darkness” of something that shocks. What makes me stop scrolling in a sea of feeds to one particular artwork, is the intelligence and complexity behind an artwork ; technique being part of it. The disturbance can be felt sometimes as if the painting actually is saying something or wants something, the artist managed to place an intention in that painting. So the artwork has become more than just a material object with paint on top of it.
As for differentiating between surreal and dark art, I think they can both meet in the middle. Some of my art I categorize as surreal dark art. But those labels are created . The artwork already exists, the labeling comes after, it’s just how our minds operate. I think the best artwork is really where you can’t even categorize it or really have trouble with labeling it somehow. That’s when something new is emerging and I think we should have that as a goal, to make true and novel work. Because this is what hits emotions, something that we have never seen before.