Lets say we had taken 1000 random people off the street in 2002 and put them in charge of a new space launch company with equal funding to SpaceX. How many of them do you think are likely to have achieved the same success SpaceX has?

To put it another way, if Elon Musk hadn't founded SpaceX in 2002, how many of the engineers currently working there would right now be celebrating working at a company having successfully recovered a first stage from an orbital rocket?

Let's try looking at it from a third angle. Lets suppose a random employee other then Elon Musk had been unable to join the company during it's history and had to be replaced with another job candidate. What are the chances such a substitution would have prevented SpaceX from achieving a stage recovery?

Finally, I'll address your proposed scenario directly. How likely is it that having the wrong mail man in that position would lead to the failure of the company? In contrast, what are the chances that having the wrong CEO might lead to the failure of the company? I can imagine Elon Musk might make a pretty decent mailman. But if we took the best mailman in the country and put him or her in charge of SpaceX, do you think that would be likely to have a positive or negative effect on the prospects of the company?