I don't understand this either. He has to trust entire layers of useless middle management to get accurate performance numbers. All he'll get are invented numbers on a piece of paper (metaphorically speaking).
The ones who leave may be dissatisfied with the artificial goals.
It is one thing if they don't talk. It is even worse if they have no experience but thousands of suggestions that don't work. And you have to debunk every of these suggestions to management while keeping the progress going.
Often, if the work horse leaves, no one is able to keep the project going or rewrite the project from scratch. They should be able to do the latter if their suggestions are so great and they have been kept back. But they cannot.
The ones who leave may be dissatisfied with the artificial goals.