Not sure I follow what you are stating Sebastion. Yes, users with edit permission for a page get permissions to create child pages, and that is the ONLY place their role permissions get default checked in the edit permissions checkbox (when they are adding a new page). But If they click on add new page from the parent page, those edit permissions don't get carried over.

And from a child page or a parent page where a user has edit permissions, that user can create a top level page (which to me is a parent in the nav menu) or child pages in other areas of the site (because the Parent Page dropdown is available to them).