I believe that HC and FDD are entirely right.
I would refer to a police officer as sir; it is simply a mark of respect towards somebody you don't know personally. I guess originally it may also have been an acknowledgement of an ATCO's "authority" in a given piece of airspace but it certainly does not imply any superiority.
In "The House", MPs are addressed as honourable members but that doesn't imply superiority either. (As I understand it, using their name has a specific meaning and purpose relating to discipline)
Point 4