I think that’s a common perception among people who see a lot of 3D Art…It’s relatively easy/fast to do except at the really high end.
You mention abstract shapes etc.
One thing I read on a blog about book covers is that preference also varies a lot from country to country, even among English language countries.
As I recall US readers like pictures/images on their covers, but Brits (or English, Sottish, Welsh and Northern Irish depending on next week) and Australians prefer more geometrical and or solid color block designs. Don’t recall Canadians or some of the other groups.
I’ve toyed with using different covers in different countries based on this idea.