Every one of those managers relied on their employees to do the necessary work for them.
As a side note, with the company I worked for, I was responsible for administering the company's UAW pension plan for our workers. After the close of our Philadelphia plant, that function was transferred to our corporate office and I was transferred there from our Detroit plant in 1997.
With the exception of one of the benefits managers who I worked for, I was the only person who understood and could interpret the UAW pension contract that incorporated over 45 years of contract negotiations and apply it to any questions that any past employee or retiree had to offer........
The knowledge I had was specific to my job and there is not an MBA grad or PHD grad that could ever match that........and I was just the lowly non educated employee that was there to handle the problems..........
So yea, MBA's are nothing but a piece of paper that is just a feather in the cap for promotions.......
I've also worked with plenty of people with the MBA who are outstanding businessmen (and businesswomen). Do I think the MBA made them smarter? Not really... most of these people were driven in the first place.
The only place I've ever seen a degree really make a difference is at the baccalaureate and doctoral levels. Master's degrees tend to be lovely parting gifts for those who fail their comps, or (as you note) people who are earning an extra stripe. Where MBAs do excel, is where they integrate their learning by taking business problems and solving them or - better yet - turning them into money.
Pauline Kael famously said after the 1972 election: "I live in a rather special world. I only know one person who voted for Nixon." Maybe you and I live in special worlds where MBAs are "nothing but a piece of paper that is just a feather in the cap for promotions" or where they tend to be driven businesspeople.