I don't understand why it doesn't apply to knowledge workers. Negotiating power is a variable quantity, not a binary property ("you have it or not"). The writers guild is a good example. Whether they use this better position for the overall good is another question. I am not sure letting all the power to the GM leads to a better result from a moral point of view. In France at the moment unions are negotiating common rules for home office (insurance policies, etc). In this case I think having unions is better for everyone.