Alexander's change in perspective was annoying, especially seeing as it wasn't actually necessary; the story of Sons and Daughters
wasn't dependent on Alexander having a change of heart. It's wartime, and a rather unambiguous war at that, where the stakes are massive - either defend yourself against the Dominion, or become vassals of the Founders. The idea that Alexander might enlist for the duration of the war therefore makes sense; they didn't have to make his earlier character arc pointless by seeming to suggest that he now wants to be a warrior after all.
He could easily have told Worf: "I still have no intention of being a "good Klingon" and I still don't care for fitting into your culture - I'm just here because I'm helping with the war effort, and this is a just war. That's all".