Since there is no real administration of grades from the student's point of view and they only see them in read only mode, It seems more logical to have the Grades link be available from the Navigation block, under the course's name. Similar to Badges. And maybe under Badges too.
This can simplify the workflow of students and minimize the need for the students to use the Administration block on a course level.
Moreover, If it is not too much confusing for the teachers who are experienced Moodle users, Let's have only one link to the Grades page from the Navigation block only, for teachers too.
It would also follow the logic we have when looking at the Participants link in the Navigation blocks and the Users link in the administration block.