“P.K. Dick was easily the weirdest of all the sci-fi writers”
J G Ballard? He was out there.
Kilgore Trout does not count.
Or maybe the earlier works of Philippe Jose Farmer, before Riverworld (which is pretty strange in a religious way).
Phillip K. Dick succumbed to schizophrenia in middle age.
J.G. Ballard grew up cracked because of his twisted childhood in Japanese-interned wartime Shanghai (see the autobiographical “Empire of the Sun” (the book is uglier than the movie). I’d put him up there with Jerzy Kosinski (The Painted Bird) although there is recent evidence Kosinski exaggerated the brutality of his wartime childhood.