Well, yes; it seems that he really had a strong fanbase, mostly among his fellow musicians. But I think you may be underestimating the popularity of Elgar, Sullivan and RVW's music (if not Ferneyhough's). I mean, these might as well be household names among relevant audiences; you can't really say the same for Britten. Now, if I had to mention gay composers who are genuinely notable for their musical output, I'd say Lully and (most obviously) Tchaikovsky.