Valid points, but every other industry has ways to assess and rank employees. Take a banker, how much did they make this year? Checkout worker, speed of checkouting. Police officer, quality of case write ups.
Pilots crash, or they don’t. How else do you assess them? Meritocracies can’t work when the only differentiator is what squadron mug you’ve got hanging up at home, which is the sort of selection that a flat system would (and does) predicate.