I think the issue is not specific to software or engineering. The best managers are those who are good at management and business and the thing their team is do

I think the issue is not specific to software or engineering. The best managers are those who are good at management and business and the thing their team is doing, in the sense that they have a team and a company because it'd be too slow for them to the work all by themselves. But they could, if they weren't under time pressure and lived forever. "MBA" is being used here as a shorthand for a professional management class who don't have any other skills, I don't think it means explicitly the qualification. And because they don't have any specific non-management skills, they think they can manage anything, which makes them mediocre managers at anything they do (at best). In other words MBA has become a label for such people because the programmes appear to promote that worldview. But of course you can get people who have an MBA and who could also do their teams work, there's no rule that says you can't. And the discussion would probably not apply to those people.