> How do you objectively (not subjectively) determine if a manager is bad? If 200 people in the organization are "happy enough", it's your word versus theirs on what a good manager vs a bad manager is.

HR should track the attrition rate for each manager. If twice as many of manager X's reports are quitting or transfer to other teams than manager Y's reports, then manager X or the projects they manage might be a problem (for employee morale and company success).

HR can also send out anonymous employee engagement surveys.