Fair point the 5% stat only reflects what people do immediately upon graduation. With that said, most of the richest people in the world have very little formal education, so an MBA is clearly not a requirement.
Certainly it's not a requirement, and spending two years getting an MBA may just slow you down and mire you in debt. On the other hand, it could be a valuable asset to fall back on if a person realizes their app isn't a real business or entrepreneurship isn't for them.
6 inherited or married into their wealth.
5 are college dropouts.
5 have only a BS, mostly business or finance.
3 have a BS and some grad school.
4 have an MBA or MS in business.
2 have some other graduate degree.
All but one of the college dropouts are in tech.