An important part of an executive’s job is hiring the right people to execute, which requires some level of skill or networking in my opinion, even if results aren’t always guaranteed.
This data says the parochial boys club doesn’t deliver any difference from the average state-school “rose through the ranks” type of executive.
He made it all because he was extremely good at playing/investing in the stock market (he never had a professional job in his life). The economics teachers would invite him to speak to their classes on a regular basis.