It really comes down to which playerbase is going to be the most active/vocal about bad stuff. I would argue that DKs have been a lot more collective and vocal about concerns. Warlock discussion has come down to myself and a couple others driving almost all of it and pretty much discussing amongst ourselves. And I'm not even a Warlock main.
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Survival mechanics radically changed with a fluid and widely loved playstyle being devolved into an incredibly choppy and jarring mess.
Marksmanship stripped to total barebones without any rebuilding like Arms was. It's near a two button rotation with talent options being nothing but cooldown fire and forgets or passives with zero gameplay interaction.
Beast Mastery design untouched, leaving it as a jack of all trades and master of all while the other two specs have been designed to have more niche strengths.
Some of the most boring talent options for any class.
There's plenty of issues for a bunch of classes but Hunters have been one of the most vocally disgruntled classes this cycle because two of their specs have been totally and completely butchered.
edit: Also note that there's been more vocalness about the state of Hunters coming from Hunters towards the top of the chain as well. Your Warlock class heroes have been staying near silent on the problems and have done fuck all when it comes to giving feedback and discussion. These are often the people who help drive discussions or draw more attention to problems and they've been nonexistent on both Twitter and feedback forums.