An economic measure of output per unit of input. Inputs include labor and capital, while output is typically measured in revenues and other GDP components such as business inventories. Productivity measures may be examined collectively (across the whole economy) or viewed industry by industry to examine trends in labor growth, wage levels and technological improvement.'
Productivity Definition | Investopedia
Whatever they are producing at their cost IS their productivity.
If they are paid 1 cent or $1 million dollars per hour doesn't matter. In both examples, they are producing the good/service with a level of productivity...the former obviously has far more productivity then the latter.
Whatever someone is paid to produce something IS their level of productivity.
So, if you are paid $7/hr. to make a widget/hr. then you are more productive then if you are paid $8/hr. to make a widget/hr..
So, by paying someone more money to do the exact same task, all other things being equal, then you are making them less productive.