Given that SpaceX lives or dies by how well their rockets work, I don't think there's really anything more important for Musk to be doing.
If your goal is to get rich and play golf and relax, that is one thing. The fact that Elon is one of the wealthiest people in the world and also as passionate as someone working in their garage seems kind of like a crazy situation.
I wonder if there is similar historical precedence in terms of an ultra wealthy person being interested and involved like he is.
I feel the key insight behind both SpaceX and Tesla is that both the napkin engineering from first principle and then having the force of will to personally see it through /are/ the most important thing. Both qualify as engineering.
Happy to have my fairy tale hero's journey view of success corrected.