If editing access is provided to an editor for specific categories / articles in the knowledge base - they shouldn't be able to create additional categories / articles (which should instead be created from the admin and then assign to relevant editors).
The need for this to be implemented with high priority is also related to all the technical URL/slug dependencies resulting from the creation of new articles/categories, and that makes it is essential to have a content role that limits users from creating new categories/articles independently.