Exactly, I don't know what the answer is (probably a combo of subjective and objective measures, along with a healthy dose of independent oversight for both) but relying completely on 'gut feeling' is an express train to unconscious bias land.

In reality I think someone who only looks at team members who are "doing the most" is really just measuring who is talking about their work the most. You need some kind of objective measures like features shipped, assigned bugs resolved, etc.