There is no notion of role inheritance or hierarchy in Moodle. Course creator is not "above" or "below" any other role. It stands by itself and does what it can do with its four little permissions. You can study it in isolation from the other roles and understand it completely.
The best way to understand Course creator (or any role) is to study (1) its permissions and (2) the entries related to it in the Allow role assignments and Allow role overrides tables. From that, you will know exactly what it can do. And when it fails to work the way it should, read the code