The hierarchical structure of your mind maps are just numbered lists represented visually. Numbered lists represented visually are useful in certain cases, but in my opinion not that much more useful than numbered lists themselves. Not everything fits neatly into a numbered list. And when you force something into a numbered list, vital details can get overlooked.
Furthermore, if I simply wanted to force a piece of text into a numbered list then I would use ABBYY to OCR it and export it to MS Word. Once in Word it’s easy to make an outline quickly and it looks nicer than MarginNote.