I disagree. The US Supreme Court ruled early on in our republic that citizens are sovereign - without subjects.
This makes it all the more appropriate that Christ is the king of kings - even of kings without subjects.
Kingship and ambassadorship have different roles. This introduces St Thomas Acquinas Odo Amoris.
Our friend,
@MatthewG, may act in in sovereign, Free man and king of self in choosing how to live his life (what clothes to wear, what to eat, what hobby to take up) and while living this kingly life also do it as an ambassador to Christ.
Being a poor ambassador does not diminish our kingly status. That is, our sovereign freedom does not depend on getting all our doctrine right, always acting with grace and never backsliding.