It's measurable in the number of times you have to spend >x minutes to help them go through something they should have written up by themselves. You can count the number of times you have to look at something and tell them "do it again, but without LLM this time". At some point you fire them.
My opinion on someone is how I decide whether I want to work with them and help them grow or fire them/wait for them to fail on their own merit (if somebody else is in charge of hiring/firing).
