"Fair" and "what you can make someone do" and "what you are entitled to" are very different concepts.
Turn this around to an employer "“Fair” is whatever work you can negotiate from the employee. You’re not entitled to any more work than you can make them do for you." - 1) if you can't make the employee do much work, you aren't entitled to much work, and that's fair. 2) if you can exploit the hell out of the employee, then you are entitled to do so, and that's fair.
Turn this around to an employer "“Fair” is whatever work you can negotiate from the employee. You’re not entitled to any more work than you can make them do for you." - 1) if you can't make the employee do much work, you aren't entitled to much work, and that's fair. 2) if you can exploit the hell out of the employee, then you are entitled to do so, and that's fair.