Performance metrics are always set against the employee. The company always wants the option to fire so metrics are set higher than possible. So if you ever meet metrics your probably cheating and that's fireable itself. It's all rigged.

Technically, if your boss supports you and likes you, and so do your other co-workers, then you’re practically immune to being fired. There really isn’t such a thing as performance-based firing, it’s more that you weren’t able to play the game as well as someone else. If you’re not liked as a person, it doesn’t matter how great your performance is unless you’re a genius—everyone has room for improvement. So performance-based firings are a problem for people with mid IQ or mid EQ, which is mostly everyone (me included). I haven’t been fired, yet but nothing to say it won’t happen in the future.

Even if the employer wasn't a total piece of shit, metrics should be able to cover the gamut of performance outcomes.

It's pretty easy to weaponize that though. The whole industry is already more than capable of producing tight deadlines for no particular reason.

Personally I prefer just a binary acceptable or unacceptable. Instead of handling merit-based increases, You do merit-based promotions. I always hated the here's the unreachable goal to get your full raise crap.