Elon's not personally designing battery chemistry or running aerodynamics simulations on bodywork at Tesla. He certainly isn't bolting them together, though that would explain the poor finish quality I keep hearing about.

The leadership of a company of any significant size can only ever be doing a small plurality of the work at most, and can usually get away with much less than that. There simply aren't enough hours in the day to outwork the hundreds or thousands of employees that are actually making the company most of its money.