No manager has direct insight into performance of 300 people (at least in tech). They have to rely on subordinate managers/teamleads, each of which can be unreliable for different reasons. Some may be playing politics, some may just be bad managers. Some will overhype their employees, some will be honest to a fault. Get them all in a ranking board, and all sorts of games get played.

If your team leads could be trusted to measure appropriately, you wouldn't need stack rankings because they'd correctly identify those under-performing. Stack ranking is conceding that your managers can't properly measure performance. Shouldn't that reflect more on management?