output doesn't capture accumulated know-how. If you fire researchers you loose know-how, hence you loose potential.
Unfortunately that means that on paper, I have zero output while the people I help have all the output. Especially in computing/data science it's easy to fall into this trap; it takes a daily check-in to make sure that I'm working on the stuff that counts for me and my group.
Also accumulated know-how can be partially visible by writing out docs, patents, guides and the like. Definitely not enough but can increase visibility.