That would make logical sense and is basically how I'm intending to run it, but I think that answer is technically wrong as far as how it's written since the adventure really tries to sell it as you can do Option A OR Option B, because the "PCs have to see that their choices have consequences". While it does allow you to do the fort first, the end result is that there will be a lot more destruction as written due to lost time.
Even though Option A makes no sense for the information that the PCs have at the time.
DM: "So, let me make sure I have this straight. You're going to turn around abruptly from your goal to chase after a creature that not only can travel at least six times faster than you, can fly in a straight line as opposed to having to follow along twisty paths, and also doesn't have to worry about the blizzards and avalanches you've regularly encountered in your travels. You don't know where it's going or what it's going to do, nor even what it is other than it looks like a dragon. You don't know how powerful it is or whether you can beat it, and odds are that since the various towns can raise dozens to hundreds of their residents as trained militia you're deciding to confront it probably won't sway the needle either way if it attacks a town."
Players: "I guess"
DM:........."You have made the correct choice.
And this is why I'm going to change how this section plays out.
It's even worse than that.
Based on the travel times laid out in the book, it's literally impossible for the adventurers to save ANY towns except for Bryn Shander, and that's only if they head
directly there as soon as they see the dragon fly out. This is contrary to the adventure text, which says that if they head to Bryn Shander first "they will be playing into Xardarok's hands" - false; it's the only way to save any town.
There is a serious lack of editorial oversight going on. The editor should have looked at chapters three and four, looked at the travel times laid out in the opening section of the book, and noticed there was a problem. Furthermore, the attempt to offer the players a dramatic, meaningful choice with consequences fails because the players are not armed with the information they need in order to make that choice. Ideally, the stakes and consequences of the dramatic choice should be clear, and there should be positives and negatives to weigh for both options. Instead, pursuing the dragon immediately is objectively the right choice - there are no negative consequences for doing so, since apparently Xardarok & Co will just sit around in Sunblight waiting for the adventurers to come and kill them. The only "drama" is that the players have to make an ill-informed choice (which really is neither dramatic nor meaningful - they're basically just being ambushed by circumstance).
I suspect that in an early draft, the travel time problems may have been mitigated by Vellyne Harpell having sleds pulled by undead dogs that didn't need to rest, but in play-testing the undead dogs were scrapped because too many players decided that undead dogs = evil NPC, and the adventure really wants them to ally with Harpell. However, no alternative means of fast travelling back to the towns was then substituted, automatically dooming 9/10 towns no matter what the players do, and rendering nonsensical text like "they can stop the dragon before too many towns are destroyed" (how many is "too many", incidentally?) and "playing into Xardarok's hands" by going to Bryn Shander.
So DMs are left to fix this in various ways - some by fixing the travel times to speed up the players or slow down the dragon, some by keeping the dragon in Sunblight until the players reach the forge. Personally, I just had the dragon attack the Ten Towns while the players were IN the Ten Towns - they damaged the dragon in Easthaven after Dougan's Hole and Goodmead were torched, driving it back to Sunblight. Pursuing the dragon back to Sunblight gave them a strong motive to actually go there, as players can otherwise put that off forever since on the face of it Sunblight doesn't look any more or less urgent that any other sidequest, and indeed as written is narratively inert until the players visit it.
My solution had the adventurers fighting Xardarok AND his dragon in the forge, which was a great fight. Yes, they didn't get to make the "dramatic choice" at the beginning of Chapter 3, but that choice is so poorly implemented that you can cut it and nothing of value is lost.
A much better dramatic choice, which the adventure doesn't really touch, is whether or not to stop the human sacrifices. Human sacrifices are bad, but the Sephek Kaltro situation suggests that screwing with them can cause Auril to retaliate. So the question of whether or not to try to stop them is an interesting one for the players, because arguably until the Rime is lifted, the sacrifices are a necessary evil. The adventure is no help in this area though, since it includes zero info about whose idea the sacrifices were in the first place, and who is in charge of them.