The OP's argument (I believe) makes an unjustified assumption that the CEO is falsely implying falsely that people who leave at 5:30 can make it to the C-Suite. That assumption lies in the subtext of an experienced, well paid, successful individual encouraging a work-practice that he did not follow himself. Read literally, the CEO is making no such claim about career (and wealth) advancement at his company beyond "you won't be intentionally penalized for leaving at 5:30."
Well, if it's true that people who leave on time can't do that I'd argue it has more to do with signaling than with actually being productive. Everything I've ever read about productivity suggests regularly working long hours makes your productivity go through the floor to the point that there is not any net benefit.
I agree with you and have read similar studies/articles.
Hours worked is a useless signal at best and a misleading signal at worst. (as an aside, I also believe the 40hr work week is a waste for both companies and employees)
Number of hours a superficial signal that it easy to imitate. People know that productive "hustlers", "gamechangers" "showrunners" get promoted. They tend to know who the hustlers are and thus they know that hustling often requires more than 8 productive hours a day of work. So they stay after hours despite diminishing returns and lower median throughput.
Once a large enough percentage of the imitators stay afterhours, now your average operational employee has to stay in order to conform to the perceived status quo.
So I agree with with the CEO leaving early as long as he enforces a culture that not only encourages people leaving at 5:30, but penalizes people who stay late. Then the hustlers will follow, and then the imitators will follow and the operational staff will feel comfortable to have their 40 hour work week.
