Comment by NovemberWhiskey

That's definitely not true. Consider the US Navy rank of commander (O-5 / CDR).

On the one hand, this could be someone who is an unrestricted line officer and a qualified surface warfare officer. This is someone who could be the commanding officer of a destroyer.

On the other hand, this could be a dentist with 20 years of experience but no significant leadership responsibilities.

The quote I've heard in the context of the UK's Royal Navy is that the same rank can be commanding officer of a ship at sea or someone who makes tea for an admiral at Northwood.