I also had the impression that Kirk was a bit snappish in this episode for no particular reason. It came across as though William Shatner was in a mood, as opposed to being something coming from Kirk. I didn’t have that impression from Spock, though. Spock’s comment struck me as being on brand for Spock. The sort of thing he would say more often, if time allowed.
Agreed. Maybe he doesn’t do it often because of time, and because of the impression you got from Spock when he said that. If Spock said things like that too often, he could come across as unlikable. Like being that person who if I say the sky is blue, they will respond with, “it’s cerulean.” They may not be wrong, but it can get tedious.