Spider Robinson made that claim in one of the Callahan books, I've been twisting my little mind to figure out who it was/is. You think John Norman? Really?
Correct on the source, and yes. I can't prove it, but look at the circumstantial evidence.
Some of the earlier Gor books were actually fairly entertaining, and there was a background story that was at least faintly interesting (Gor is a planet in Earth's orbit that we can't see, you see, because it's always on the other side of the sun. Some nice aliens run Gor, but some evil aliens are trying to take it over. The nice aliens and some of the humans on Gor are trying to stop the evil aliens. They occasionally swipe women from Earth to keep the supply of slaves up. Other than the slave angle, they were similar to Burroughs but not as entertaining).... Anything after the eighth or ninth book in the series was completely unreadable, with page after page of female slave subjugation scenes interrupted occasionally by some minor plot advancement.
I always thought the Spider Robinson quote referred to the Richard Blade books, some of which I had the misfortune to read long ago - they made Norman's books look like Shakespeare.