Well, when you put that way - yes, this won't work when dealing with Batman, but the important thing here is not the specific trick - like the kick in the nuts - but the main principal. And it's the fact that while The Joker shouldn't - he can't - dominate the fight, he still must be able to hold his own, even for a second or two, via all kinds of unpredictable, unfair and nasty tactics. A good example is the fight from 'The Killing Joke' - Bats was hammering Mr. J big time, but he used his acid flower, then pocked his eyes out, a bit later tried with the gun - and while he still lost the fight and the dominating one was Batman, at least I, at the end, had the impression that The Joker was a pretty dangerous guy.