I have not read “The Brains of Earth”, but if it pre-dates “Dianetics” then I think we have a case of plagiarism!
My dear late husband was the BIG sci/fi fan. He once wrote a personal letter to Joe Halderman and got a very nice personal letter back! :-)
(for those who don’t follow sci/fi, Joe Halderman was not the same as the Halderman in the Nixon Administration...different guy.) LOLOL.
I have heard of the the ‘forever war’ by Joe Halderman, never had a chance to read it yet.
I think the first dianetics articles Hubbard wrote came out in Astounding Science Fiction Magazine in 1950. Wiki has the first mention of thetans in 1951. I can’t find any mention of the ‘Brains of Earth’ coming out in a magazine, but I would think if it did it would have been after 1950 for sure. I think it was probably just Vance poking fun at Hubbard, although I can’t find any mention that they knew eachother. It might have been strange had they not, I don’t know.
Jack Vance is 97 years old, probably my fav.
Freegards