I believe the admin setting for "Sort My Courses" only applies to the "My Courses" menu and not the course overview block. I am baffled on how to force the display of enrolled courses on the course overview block.
This is now an optional plugin (as of Moodle 3.3). https://github.com/thepurpleblob/moodle-block_course_overview
Stick a request in the 'Issues' to remind me and I will add that feature.