I did not know that about the script.Mitchell was not the XO in WNMHGB, Spock was. It was in the script and Nimoy was costumed accordingly.
I guess I had thought the notion that Kirk asked to have Spock made XO because of his value in that incident had been made ... retroactively official? That the costuming "error" was simply to avoid having to make nimoy a shirt just for the pilot.
I didn't mean to suggest anything like the ridiculous extremes to which nuTrek rises. I meant that Kirk benefited from rare exceptions.He's not a superhero, that's a nuTrek type of thing. In TOS Kirk was clearly young for his job, but it wasn't implied that the rules for mortal men didn't apply to him.
As an example, in TNG Data says an officer could expect to spend 12 years "in the Lieutenant grades". Riker clearly did not, as less than 12 years out of the Academy he's already a Commander.
More aptly Stephen Decatur was recommended for promotion to Captain without having commanded a vessel, although he was placed in command of a ship before confirmation of his promotion came back across the Atlantic.
To me the idea that Kirk had no command before Enterprise is almost to imply that there are no smaller vessel commands in Starfleet. If there are, who is commanding the destroyers, frigates, scouts or what you will, if not officers like (Lieutenant Commander, Commander) Kirk? Why would Kirk be not qualified for command of a smaller ship at that point of his career, but then be qualified for one of the high-prestige starships?
The assumption (and it certainly is just an assumption) is that Kirk, like the people/characters he was partly based upon (Horatio Hornblower and Stephen Decatur, notably) repeatedly committed acts of great distinction, and moved up the ladder by bounds.
Certainly the other people we've seen in command of similar ships all seemed older than Kirk.
So while Ben Tracy probably commanded a string of smaller vessels as a Lieutenant Commander, Commander, and Captain before being given the Exeter, Commander Kirk may not have paid all those dues.
Stephen Decatur's first command was, IIRC, a vessel he had captured from the enemy. He was put in charge of the boarding party, not really intended to be given permanent command of a ship.
Kirk did something awesome. Not "let's make this cadet CO" awesome by any stretch, but something that said "this guy is ready for a command, an important command." And then Chris Pike gets tapped for promotion, and the Admiralty (or Starfleet equivalent) is wondering who to get to fill his chair. And somebody says maybe that's two problems with one solution: give the Enterprise to Kirk.
Like how for the battle of Midway, command of the carrier task force was given to a cruiser captain who had never commanded a carrier because Admiral Halsey said he was the best man for the job.
As I said, this is all just my feelings. If your feelings disagree I can't fault that. Certainly I would expect most Starship Captains commanded several smaller vessels first. But Kirk seemed attached to the Enterprise in a way that suggested she wasn't just one of many ships he'd commanded.
(In fact, Kirk's attachment for the Enterprise may be a good argument against promoting people directly to the big ships. I recall a TNG era novel where a character feels that Kirk was too young to be in command, citing several TOS episodes as stuff he clearly just made up. )