Thinking about it today, I realize the central issue with this episode: It's Korby's story, not Spock's story.
It's established late in the episode that "Trelane" is just doing all of this to fuck with Korby because he hates him. That's why he wipes Spock's mind like everyone else, but not Korby. He set up a scenario to make Korby suffer, and giving Spock the "happy ending" was just a side effect. "Trelane" wants to see Korby squirm and suffer as he "gives her away" to another man. He's the one who has something to lose here - he's the one with the stakes.
Does Spock show growth here? I mean kind of, because he seems "over" Chapel to some degree by the end of the episode. But there's never a point, once he gets his memory back, where he considers for a second that maybe he should let Chapel remain mind-controlled and marry him. There's no real internal conflict here to his character. He barely even gets a moment of self reflection to think "I wanted this, but not like this."
The issue is, it would have worked so much better if only Spock knew about it, and not Korby. Because then he'd be the one who makes the affirmative decision to reject what "Trelane" was offering him, rather than trying to go along with Korby's plan.