As you delve further into the article, and (ironically, based on the topic) consider the ideas presented, it becomes more clear. Or skip to near the end to see.
TLDR: AI and generic pop culture artifacts have something in common - a lack of a certain type of depth that makes art great.
I think that's not the author's point; he's mostly talking that time solidifies ideas as shown by the evolution of points of view. At the same time, his picture of the wave shows that over time the painting feels more distilled and simplified. So is his point actually that simple ideas persist and are appealing? It isn't clear? That an art improves?
I think slop-pocalypse misses one thing. AI's time of thinking is very different than ours.
A "thick" argument that could take a lifetime in human terms could happen in minutes of AI.