We practice uki-otoshi to learn how to get power from extending the open side hip, this video can give some pointers. Float uke up first, then throw him over his front foot by drawing hikite to the open side hip. Notice how both the first two exponents extend both their leg and hip on the open side. Finally Mifune turns as he does the nage no-kata uki-otoshi - I thought it was just us aiki folk that did that.
I was wrong in saying that it was likely that nobody had ever won a judo bout with uki-otoshi. It works fine as a counter: