A reasonable test of 'productivity': if you fire large swaths of employees and 'productivity' remains the same, was it a failure of management, or of the employees?

I'm just kidding. Measuring employee 'productivity' is one of the biggest hand-waving magical misdirection performances in business. The mistake is employees think it means 'working hard' or 'smart', or whatever. The truth is it doesn't really mean anything, but too many people are heavily invested in it being a thing.