I think it's a bit of an overstatement to say that the Season 1 arc was already worked out before Fuller left. We know major sections of the series - like Lorca being from the MU - were added later.
Yes, I did already acknowledge those changes. My point is that the basic idea of spending the whole season on the Klingon war was kept, even though the specifics were refined. The term "arc" refers to the overall storyline, not every exact step along the way. If they'd wanted, they could've decided to wrap up the war sooner and spent the rest of the season on something else; arguably that's kind of what they did do with the massive Mirror Universe arc in the second half, so it wouldn't have been much of a stretch beyond that to wrap up the whole war in episode 9 and do something different for the finale. But they still stuck with the original plan to continue the war arc until the end of the year, keeping the basic idea even while changing the details.
Also, obviously it's just my opinion, but the season finale was so lackluster in its final half that I simply cannot believe they planned for the season to have ended that way from the beginning.
Not in the specifics, obviously, but in the broad strokes. Don't think of it as a single step. That's not how writing works. You start with the rough idea for the season's arc (Klingon war, Burnham's disgrace and redemption), then you break the season by figuring out what broadly happens in each episode (e.g. "This is the episode where they make the drive work" or "This is the episode where Lorca is revealed"), then you break each episode by figuring out what broadly happens in each scene, then you write the actual scripts and come up with the specific lines and the specific way the scenes happen. Then you rewrite and rewrite and rewrite some more, and eventually you run out of time and are stuck with whatever the most recent version was. Each new layer of decisions refines how you advance toward the goal, though the overall goal remains basically the same.
Regarding Season 2, given Kurtzman is hiring someone on to manage the writer's room, that seems to indicate that a great deal of writing work still remains for this season - that whole scripts have yet to be broken.
That doesn't follow at all. First off, Kurtzman brought in Duff to help
him run the room. Kurtzman is the main showrunner at this point. Second, breaking the scripts is just the very start of the process, like outlining a novel. The whole staff is involved in every stage of the writing from beginning to end. Scripts are assigned to individual writers, but the whole staff is then involved in the rewriting process.
Third, even writer-producers have responsibilities beyond the writing itself. This is a business, and they're management. They have to oversee every stage of the creative process, and that includes aspects of the process that don't get onscreen. As we saw with Berg & Harberts's firing, there are factors of budget, personnel management, and other business considerations that are part of a producer's responsibility independent of the content of the scripts, and a full staff complement is needed to handle all those behind-the-scenes management responsibilities so that the scripts can be produced smoothly and on schedule.
Here's a PDF essay by Javier Grillo-Marxuach (
The Middleman, LOST) about the business of writers' rooms and showrunning:
The Eleven Laws of Showrunning
It explains how the modern writer's room is not merely a mechanism for creating scripts, but a mechanism for cultivating future showrunners. It's a systematic hierarchy designed to train writers for progressively greater responsibilities until they reach the level of creating their own shows or founding their own production companies. It's all very structured, and it's about a lot more than just the scripts themselves.
And
here's an io9 article in which a bunch of showrunners talk about writers' rooms and how they operate.
I should also say that since part of the reason that Berg and Harberts were fired was due to blowing the budget early in the season, it's almost certainly the case that whatever plans existed for the back half of Season 2 will have to be severely curtailed. Thus it's likely that we'll still see considerable drift from their plan - presuming it was anything more than a few paragraphs to begin with.
But it would be
more expensive to throw everything out and start from scratch than it would be just to find a more economical way of telling the same stories they'd already been making plans to tell. Again, even if they change the specifics, the broad strokes of the story arc for the back half of the season will probably remain, and it'll probably end up in basically the same place as originally planned even if the path to get there is different.
It's been said that writing series television is like building a car while it's racing downhill, or trying to fix a runaway train. You don't have the luxury to stop everything, do a rethink from scratch, and start over. You have to do everything on the fly, on a time limit, and it's hard to change direction once you're underway.