HR is NEVER your friend. They are not on your side. DO NOT TRUST HR.
Anonymous feedback is never anonymous. DO NOT TRUST HR.
Here's the deal... Exit interviews, as a manager, were annoying because they could ding me on my annual reviews. And that's fine, except... people would complain about things I had no control over. "Oh, my manager made me do something stupid that I didn't like!" Yup, I get it. Only it wasn't ever me making them do that, it was my boss, or a client. And still, as the manager, I'd get blame.
And you know what I did with that information? Every time someone trashed me, or the company, in an exit interview, I'd remember it. And 2-3 jobs from now, when you need a rec, or you need someone to say something nice about your time at my company, I'd be unavailable. Or if the new place you were applying called, and asked me, "Do you have any feedback about X candidate?" You better believe I had things to say about the people who were negative.
The advice in the post are spot on. Keep your mouth shut. Odds are it's not your boss that's making the bad decisions. Odds are the culture is exactly how the people at the top want it to be. Anything you dislike, it's likely out of your manager's control. Trashing them is just a sign you don't see the big picture. And bosses are petty, they'll get revenge if they can. And odds are you'll need them to say something nice about you at some point.