Thanks for responding!
"I had created learning paths as activity waterfalls" You don't say what type of activities you used for those learning paths: quiz questions, lessons, pages, other?
"I do not understand why it is technically possible to import questions from the question bank to a lesson activity, but not to export them to some format like XML, or to export them directly to the question bank."
As I explained in my previous answer, this is not possible because the Lesson activity programming is totally different from Quiz and the Question bank. The fact that some (actually only a limited set, as you found out) of the question types in the Question Bank can be "imported" into a Lesson activity results from a "hack" which only works one way.
Finally, you say you used the Lesson activity for its branching features. Would you use those branching features for your exam Lesson as well? Have you thought about using some H5P activities, such as Course Presentation, Interactive Book, Branching Scenario, etc. which might suit your purpose?
