And you're kind of missing the point of the complaint. The thing isn't about slavishly following Morrison's take on the character, as you mention that was already shown not to be the case. At the end of R.I.P. Joker goes missing with Batman and his reappearance to the Batverse, especially as there is a new Batman, should be a huge thing, no matter what the incarnation is.
Instead they have him show up here, not even seemingly bothered about Batman to throw a jealous fit over Harley. So they fail to take advantage of that dramatic opportunity unless people are arguing that Harley is more important to the Bat-mythos and Joker than, you know, Batman.