That’s for maxxed out knowledge work. Most of running a business is simply doing mid grade knowledge/admin/management work in a responsible, cares-about-the-outcome aligned fashion, which you don’t get from some $50k/y admin person or middle manager.

I would say that less than 25% of a startup CEO’s workload requires the “well-rested, highest quality thinking” that you describe. A lot of it is simply quantity and determination. The output of “having grit” is not that you are suddenly smarter - it’s that you are less willing to stop.