At some point we (society at large) are going to realize these fluffy c-level people are toxic and remove value from companies - then, ideally, we'll move back to a default of promoting internally.
It seems that some of these fluffy C-level people are actually good at their jobs, but we haven't found how to reliably distinguish them from the fluffy C-level people that slash and burn everything and juice the stock price with buybacks and financial engineering, then ride it out until a catastrophe happens.
One of my requirements when taking on a job (and I work in smaller companies) is having a sit down with the executive and making sure they know what they're doing - after googling them and making sure they aren't just the child of some famous person. Being in a c-level position and having a famous relative is a bad sign for the company.
My cohort has Civil Engineers, Materials engineers, Physicians, Finance, Accountants.. and also art students and communication students.
All this to say you can't generalize a whole degree.
MBA is a set of methodologies that are hilariously unfit for purpose unless your business is about making widgets in large volume.
Muilenburg was promoted internally.