Wouldn't say that, there is a huge shift in art style between what we got before Photoshop and what we got after. Just look at book covers in the 1970/80s and book covers in the 1990/2000s. The old stuff was full of custom illustrations, while the new stuff is often just copy&paste of generic stock images or some rather hideous early 3D renderings. Even the bad covers of the 80s (see /r/badscificovers/) still have some personality to them that is lacking in a lot of more modern ones.

It's not that you can't create good art with any tool, it's just that the economy and expectations change with the tools available, and the tools being faster/cheaper doesn't translate into better art.