I think the analogy holds for the case of employees not having the capacity to give extra hours due to other commitments. However, I totally agree that people aren't AWS servers, and the reason I felt the analogy was bad was that such a mechanistic view doesn't leave room for the multitude of positive, human ways of working around such problems. For example: if an employer asks a 20h/wk employee to work extra hours, then there can be a negotiation around whether the extra hours can be done at home, flexibly in the evenings, or for a higher hourly rate. In other words, people can compromise and negotiate a settlement which is beneficial for all.

I also don't think it's necessarily true that two part-time people would be less skilled or less focussed on work. It's the very point of the original article that working fewer hours can increase the quality and focus of the work done during that shorter period.

I've worked with many talented and exceptional "family guys" (and family women) who were skilled and totally focussed during working hours. I haven't noticed a correlation between people's priorities outside working hours and ability to do good work.