I've been thinking about this recently, what if we're doing it all wrong? what if, instead of your manager giving their reports a review, and then also giving raises based on that we go with a more market-based approach. Hear me out:

Every year, and once a year, all the managers in the company submit bids to the employees that they want to work under them. Employees then select their favorite bid, and that becomes their new manager. Employees are free to accept/reject bids based on any criteria: Salary/PTO/On-call requirements, etc.