You basically just said "this perception might be wrong but it's one we criticise anyway", which... yeah.
In any case, MBAs can help start-up focused entrepreneurs. They can be start-up focused entrepreneurs. Your perception that it can't be so is exactly what I'm talking about.
I was intentionally ambiguous. Of course an MBA can do those things, but MBAs don't start in their parents' garage. Steve Jobs didn't have an MBA. Larry Page and Sergey Brin only have honoraries. David Karp of Tumblr didn't get an MBA. The ideas just conflict, so it makes us dismissive for no good reason.
In any case, MBAs can help start-up focused entrepreneurs. They can be start-up focused entrepreneurs. Your perception that it can't be so is exactly what I'm talking about.