I second this. You'll almost never convince upper management the smooth-talking buddies they promoted could ever possibly be terrible to their employees.
Well, you could. It sometimes works. The problem is when the manager who manages your shitty manager moves away, and you get a new one. Good managers always get promoted or move away, only the terrible ones stay. The shitty manager will start afresh to get onto you.
They’ll believe it alright, and then laugh about their silly peon’s protest together.