Your stated argument would make sense if you're dealing with reasonable people. Which is sometimes.
But I'm talking specifically when shit hits the fan and people levels above me put down a mandate across many divisions.
As it is if they're making cuts they'll grasp whatever metrics they can and cut. If they don't have metrics that gives less protection, not more.
Take "as you can see I have X number of staff fully allocated and up to their eyeballs in work" vs "I don't have that metrics but trust me". That's part of my job or responsibility depending on my seniority to justify my team and keep them employed and not stressed by cuts and workload.