Re: does a starfleet ship always have a CO with the rank of captain?
I was always curious about the presence of "Commodore" Decker on the Constellation. Even though the grade of Commodore is no longer used in today's Navy (having been replaced by the absurdly-named Rear Admiral Lower Half), IIRC that title was usually given to a battlegroup commander (Fleet Captains were also referred to in a similar fashion). Commodore Leslie in "The Ultimate Computer" fit this tradition much more accurately, having been the flag commander of a battlegroup of 4 Connies against the Enterprise. Decker was just floating around out there on his own, in what could arguably be a much older not-so-ship-of-the-line Connie or Connie variant (don't want to engage in a debate on registry numbers, though). I wonder if he was like Adama in NuBSG - too tied to the service to retire and Starfleet didn't want to completely embarrass him, so they sent him out to pasture in a broken down older ship in a region where (they thought) he wouldn't get into much trouble.
I may appear unoccupied to you, but at the molecular level, I'm really quite busy.