You are right, the permissions are not easy to set and our intention is to change that and to make one place for setting all the permissions, as you suggest. Also, you will be able to set them locally as it is now.
Moreover, our intention is to make one more view for permissions - to browse them by task, not only by role. Example: 'Who will be able to edit blog posts?' (you have to select roles: administator, blog editor, blog writer, etc.)
the Telerik team