I had to think about this really hard and then realized Ursula is at least most plainly the kinkiest, we just don't realize it because she's not an attractive human.
She's keenly sexually aware and manipulative, voluptuous, practically wears a latex suit, is a sadistic dominant with two loyal and devoted servants, and deals specifically in relationships for a living. A lot of the villains have these characteristics but lack the clear, outward sexuality that we see Ursula display, especially during her song-and-dance routines.