Updated: Comment #N
$storage_controller->getQuery(), but without checking for ConfigStorageControllerInterface first. This prevents any other entity storage from being used.
Additionally, the other storage controllers bypass the getQueryServicename() method, and just use \Drupal::entityQuery() directly.
Move getQuery() to EntityStorageControllerInterface, and use it.
User interface changes
API change: All entity storage controllers must have a getQuery() method. This is mitigated by the default implementation on EntityStorageControllerBase.