Currently, to access the overview of question banks you need to have moodle/course:manageactivities which seems wrong.

If I assign the role "teacher" to a student on a question bank the student should have access to the question banks overview page.

IMO capability check should not check for moodle/course:manageactivities but instead check if for every question bank in the course the current user has one of the related question edit/view capabilities.