I'd rather be at the mercy of _relatively_ objective metrics than at the mercy of whoever my boss happens to be. (I happen to like my current management chain, but people come and go...)
What? The metrics should be distilled from the overall company/org/team goals and mission and if you're working on things that don't align with those of course you're not going to have a good performance review.
I left my previous team partly because we went through three managers in less than a year, and I rarely saw them. I assume the performance feedback for the team was effectively nonsense.