I have been to these type of clubs that you mention ( out of curiosity )Then what are you talking about?
I'm a shibari expert and I do kink with very attractive women. I don't 'rate' women, but most rope bunnies are slender 20-30yrs and into yoga/dance/martial arts in order to be flexible enough to be put into the kind of positions I put them in. I think women tend to be adventurous with those men who instil in them a mixture of safety/excitement. Many of these pretty girls like to do these kinks in the privacy of my lair, but plenty of them also enjoy being watched in kinky clubs as I tie them up naked and spank them until they're glowing, so I disagree that kinky women are mostly average looks. At the clubs, you see all sorts, from obese 50-year olds to slender 18-year olds.
The only above average looking women ( and even men ) ones were actually escorts
Plus the average age of non escort people is quite high
I think that every guy who has been to these type of places will say the same thing