If 5 people including a janitor produce 1mil in profit. And having 4 people, no janitor makes 600k in profit due to having to work in filth and taking breaks to clean up then the janitor is worth 400k. It's not really that complicated. Capitalists like to pretend these things are complicated when they're not. Companies have a damn good idea of what their janitors are worth because it's constantly compared with what they cost to see if they can do without them or outsource them to a contractor.

When it comes time to PAY them they don't care what they're worth anymore, just how little they can pay someone to do the job.