Your stipulations are not based in how the world really works, especially for large organizations. Nobody has a fantastic hiring process and an unlimited pool

Your stipulations are not based in how the world really works, especially for large organizations. Nobody has a fantastic hiring process and an unlimited pool of high quality candidates. But in that fantasy situation, you've designed a company where everyone is with the company for 10 years (unless they voluntarily leave), and where your overall quality level is amazing and always increasing. It sounds like there are worse problems in the world.