Map and outline side by side
I feel and use the outline view as a kind of table of contents and control view. I therefore suggest that you can optionally open it next to the mind map instead of just being able to switch from one to the other. The outline view would be a bit like the tag hierarchies in PDF files and would be very helpful in this way too.
In this context, it would probably make sense to introduce an additional option: the user should be able to choose whether opening and closing the branches should work synchronously or independently in both views. This option should be easy to change while working because needs can change quickly.