I can summarize what both the original author, and what the person wrote criticizing agree on. Yes, sleep is required. Get enough sleep that you feel rested.

A lot of the critique was around the 8 hours, and the conclusions about what happens if you get less.

Anecdotally, I never sleep 8+ hours. I also get up without an alarm clock every single day. I'm not going to stress that I normally sleep ~7 hours and feel rested when I wake up. I know on the rare occasions if I get less than 6 hours, I'm going to be really tired that night.