Error logging seems to be broken

It seems error logging is unable to work:
https://git.drupalcode.org/project/mailchimp_ecommerce/blob/8.x-1.x/mailchimp_ecommerce.module#L94

/**
 * Logs an error message using watchdog, if enabled.
 *
 * @todo This function cannot run, the function "watchdog" is never defined.
 *
 * @param string $message
 *   The error message to log.
 */
function mailchimp_ecommerce_log_error_message($message) {
  if (function_exists('watchdog')) {
    \Drupal::logger('mailchimp_ecommerce')->error('%message', array(
      '%message' => $message,
    ));
  }
}

Notice the @todo. I am not entirely sure why we would want to have this function at all rather than just injecting the logger service where needed. I think that would offer more flexibility, as this is only logging errors, and there could be other places we would want logging. For instance, there are a lot of drupal_set_message where a log entry might be more appropriate.

How do we want to proceed here?

1. Fix this function ( remove the check for 'watchdog' )
2. Remove this function and inject the logger service