I got that feeling too, and I can't lie just because it's a mandatory thing to hate on Jared...
The complaints are justified, but I don't blame Jared. We know there were different takes and we know the tone of the script was meant to be darker, and we did see scenes that will never see the light of day that shows Joker being an absolute evil bastard towards Harley, as that was in the original script. In that script, and I suspect in the many takes done for it, Jared pulled off something darker and creepier...
But once WB stepped in and laid down the demands on Ayer to lighten up the tone, he had no choice but to go with Jared's goofier takes, cut out and reshoot any scenes that were remotely "too dark" for audiences, and shortening his screen time, thus botching up Joker's character and Jared's performance. It was still an iffy script at times, but the wounds inflicted would've been absolutely less severe or even non-existent, had it not been for that meddling.
I'm willing to bet Jack and Heath had bad/goofy takes on scenes. Imagine if WB forced Burton and Nolan to go with their less threatening and sillier takes in the more darker scenes...