It depends if the manager is actually interested in measuring performance or if the whole exercise is just box ticking. There is nothing wrong with subjective

It depends if the manager is actually interested in measuring performance or if the whole exercise is just box ticking. There is nothing wrong with subjective measures provided what is being measured is performance and not something else. Assuming a manager is not totally clueless they are able to subjectively measure performance just as well as the rest of the team. Everyone on a team knows who is pulling their weight and who is being being pulled along. There are course edge cases where some people go unrecognised or other get the credit, but in the main most people know who is contributing and who is not. The real problem is that actual performance is rarely even subjectively measured.