It seem to be the consensus that Dini's recent (last five years) work has been passable to poor with the exception of his Joker issue of Detective
I'm not sure where you get your consensus from, but that's not the vibe I've picked up at all. Praise for his Hush arc alone was pretty high, and many considered that character irredeemable.
It's not so much the editorial mandates (because there were not many, and none regarding Jason Todd)
That doesn't tie in with what was intended for Countdown. Since Infinite Crisis, Dick, like some others, had been haunted by a shadowy shape going on about "You should be dead" and "You should have died when you were supposed to", that sort of a thing. Now since Dan Didio has a plausible alibi for those occasions, it was foreshadowing for something, and from what I recall it was for him seeking out what was meant by that in Countdown, accompanied by the similarly haunted Donna Troy.
Jason Todd being featured required an implausible and never explained personality volte face, which didn't work and didn't stick, even within Countdown.
I agree Zatanna risks over exposure in the Batverse, but as long as it's fun I don't find it any more irritating than Superman constantly showing up.
Perhaps I have been lucky, but I genuinely haven't felt any particular groundswell that Dini wasn't having a good run.