At most he wrote one volume's worth -- whether we trust E. F. Bleiler's compilation for Dover (only 12 stories) or the somewhat larger S. T. Joshi compilation for Chaosium (a few poems, ~22 stories, 1 novel) -- but horror/weird stories were certainly not his main subject. It's one of those writer's ironies (anomalies?) that what made him famous and popular has faded away while he's remembered, if at all, for less than a handful of stories from The King in Yellow. We could say something similar about F. Marion Crawford and probably a few others I'm not thinking of at the moment.
I can't speak to the quality of the other stories in either the Bleiler or the Joshi, except to add "The Court of the Dragon" is good, if not as disturbing as "The Repairer of Reputations."