In 1965
1964.
you had a producer who spent the near equivalent of a small movie budget on a pilot for a new science fiction series whose premise was an Earth ship exploring the Galaxy.
So, what do you do for your introductory episode? You have the Captain (and main character of the show) already burnt out on exploring the Galaxy, and seriously considering quitting the service, etc.
^^^
In my mind, if I'm an interested viewer, seeing that wouldn't give me much faith it the show's premise of longevity. The first episode, and the Captain is already burnt out about his career?
No, that's just where he begins the story. What matters is where he is at the end of the story. I don't see anything wrong with a story that shows a character starting out in a bad place and ending up in a better place by the end. Many pilots are structured that way. Like various buddy-cop pilots where the cops start out hostile to each other but bond by the end. Or, to offer a rather facile example, superhero pilots where the characters start out normal and then get superpowers, and are initially reluctant to take on the heroic role but then come around. What matters in a pilot is where the characters are when it ends. It's expected that they'll follow some kind of an arc to get there. So I really don't see the problem here.
Christopher is right in a general and factual sense, but the charisma gap between Hunter and Shatner is like the Grand Canyon. Star Trek dodged a bullet when Hunter bowed out.
There's a similar difference between the actors who play Dylan Hunt in Roddenberry's two tries at a post-apocalyptic pilot, Genesis II and Planet Earth. The former's Alex Cord is prickly and aloof and brooding, while the latter's John Saxon is much more accessible and charming and would've made a much better series lead. It's practically Hunter and Shatner all over again.