Some of these problems exist in any company, but at least in a standard hierarchy, if your boss is sabotaging you or ignoring you, there are routes you can take (go to their boss, go to HR) to (imperfectly) route around that. In a flat structure, you're grasping at ghosts - after all, no one's your manager, so it shouldn't matter if one person has it out for you, but of course, if they're politically entrenched, it absolutely does matter. And there's no one in the company to complain to, because the company's official position is "this is impossible, we're a flat company", and your complaints are minimized if you complain externally, through some combination of "sour grapes" + "but it's a flat system!".
Honestly, it's a great trick on management's part - everybody has the responsibilities of management, but no one is an official manager, and there's an easy playbook to run on anyone who complains.
Any "objective measure" that a regular company uses is mostly a way for management to pose and bluster about what they actually want. Corporations are fundamentally all the same.