You can’t measure a knowledge worker but we can assess someone as a person, not a machine. The team knows who is not pulling their weight. If we have good relationships they may know why too, and sometimes be able to help.if that doesn’t work, it is their personnel manager’s responsibility to find out why, once it is brought to their attention, and to find ways for the person to flourish.
When a plant doesn’t grow well, first water it. Then change the soil conditions. It may need some support. If none of that works, try moving it somewhere better. If none of those work, weed it out.
Many work cultures are way way too quick to eject people, spitting out lots of institutional value and sending a really bad message to those remaining.