His over promising and under delivering to the investors is a side effect of creating crazy stretch goals for his engineering teams. He knows engineers will take all available time available to overthink and overplan every situation and that unforeseen delays and problems will eventually pop up. So he sets unrealistic goals and timelines to push his engineering teams to do the impossible in record time. He definitely doesn’t hit the milestones he sets, but he for sure gets there faster then if he actually set realistic timelines from the get go. Believe me, his engineering teams hate it to, but all admit it’s an effective way to do what he does. This works “fine” for a private company where there are no public share holders to beholden too, but breaks down when it’s public because he has to keep up the crazy goals and timelines with everyone.
If you add 5 years to “Musk time” you’ll be better off from an investors standpoint.