The problem here is that the Joker has been handled differently by different writers.
Azzarello & Miller have said the Joker is not funny -- his name is ironic. (Granted, Miller's ASSBAR Joker is...... just... ugh.) And so that's how THEY'VE written him.
On the other hand, Dini and Dixon (among others) have written him in a way that's been very much black humour. We laugh at what he does, then we take a step back and think... "Oh. Should I have laughed at that?"
And yeah, I agree with you 100% on Countdown. That was atrocious and the parts with Harley & Holly were cringe worthy b/c frankly there was no point to it at all. Especially given that I've never ever seen Harley attempt to be a hero. She just plays the game coz it's fun and does w/e she wants. I didn't entirely enjoy the way her character was used during it.