I can't comment on context switching, but one thing to keep in mind is that 40 hours is the peak of a bell curve. That implies that some individuals can in fact work 50, 60-hour weeks for months without a significant drop in productivity, and some probably shouldn't work more than 4 days a week. Maybe Elon Musk is the one-in-a-billion guy that can actually stay productive for 100+ hours, but thinking that's reason for you working 50+ hours is like saying you should be able to swim 100m in 70 seconds because they do it in less than 50 in the Olympics.