Not prepared to dismiss lack of TWD out of hand, but I suspect the loss of The Conjuring hurt attendance as much if not more. And the supporting players--a show from a cable network no one gets and a difficult-to-process, sequel-free movie from 37 years ago--didn't really make up any of that ground. Said before, but there really is a limited universe of universally beloved horror IPs. To keep up the current model, probably need to start expanding to more sci fi (e.g. Alien), maybe fantasy (Labyrinth? Legend?) or even comedy (Ghostbusters? Beetlejuice?).
Then again, AHS hasn't been pulling the multi-hour lines this year, either, and that's the closest thing we have to a "control" in this equation. Word around town (can't vouch for source, why I hadn't shared) is UOR is down 6-8% this year. If guests, particularly APs, aren't going to the resort, probably not making the extra effort to go to HHN.