Has art jumped the shark after WWI?

[Nope]

Stephen King is considered pulp mostly because of his writing style. He's good at weaving a story and great at developing characters, however, his delivery is fairly pedestrian.

In writing, plot and character are everything -- and sketching out a character with words is an art unto itself. I disagree that his delivery is pedestrian, as well -- there are moments when his writing is perfectly electric with energy.

I think he's considered pulp because he writes two or three books a year, and sells them by the boatload.

I can not copy or paste his work so I am going to have to type this directly from King's book, The Dark Tower. My contacts are bothering my eyes and I have poor eyesight so hopefully I didn't mess up in copying this from the book. Remember, this is a world that he invented for his fantasy series.

The desert was the apotheosis of all deserts, huge, standing next to the sky for what looked like an eternity in all directions. It was white and blinding and waterless and without feature save for the faint, cloudy haze of the mountains which sketched themselves on the horizon and the devilgrass which brought sweet dreams, nightmares, death. An occasional tombstone sign pointed the way, for once the drifted track that cut its way through the thick crust of alkali had been a highway. Coaches and buckas had followed it. The world had moved on since then. The world had emptied.

I like King's writing style but I admit, he has improved drastically as he gets older. Anyone who can invent the monster in It or fashion the world in the Gunslinger series is very creative.