So...I guess I disagree with the premise. There is no single educational achievement that anyone can get that will single-handedly assure success in their career.
Have there been many success stories of people with MBAs? Yes. Have there been many success stories of people with law /medicine/accounting degrees? Yes. Do each of those guarantee success. Hells no.
Does an education guarantee success? No. The only thing that guarantees success is determination to be successful.
For me...my MBA taught me how the world works. It is surprising how few people understand how it truly works - yet they speak as if they know. For that single achievement alone, I would encourage everyone to get an MBA. That being said, does that mean that everyone that gets an MBA understands the world? No. I think it was more my finance/economics slant that did that.
Even still...does everybody with those slants achieve the results I did? Absolutely not.
So as I said.....it's not about the single data point that will make you a success - it's more than that. Survivor's bias (not sure if that is the correct term here) does lead people to link the two - i.e. the people that are more likely to be successful are the ones that are more likely to get a degree like that.
That being said...all people who get those degrees won't be "successful" and all successful people won't have those degrees.