The implication that smart people don't desire the balance to be with their families every day is bizarre.

Well from experience of being an undergrad and going to career fairs, this assessment is spot on. You don't realize this whole thing is bullshit until a few years into your career.

The implication that the best engineers are just the smartest people is, likewise, bizarre and doesn't track with what I've seen.

Because my frame of reference is being early or maybe early-mid career, where you can't possibly have the necessary experience to be 'best' without working significantly more than 40 hours weekly, and from my perspective most of getting there in the future follows that path too. I'm not discounting that some top engineers could exist outside of working a lot, but for most people the path to that distinction is a lot of work, and in most places that lot of work gets done outside of the hours when people are distracting you with meetings and small talk, which means not stopping at 40 hours weekly.

Having said all that, I don't discount the possibility of work life balance in the 60-80 hour range, but that's a whole separate skillset.