I hear you. The problem, I think, is that you'd end up having a "story" (in this case by declaring the entire series one storyform) in which for the vast majority of the pages or screen time we weren't looking through the eyes of the MC.
Maybe another way to look at it is that there's this "title" story (i.e. the thing that we call "A Song of Ice and Fire" in the case of the books or "Game of Thrones" in the case of the TV show) which is made up of snippets from all the books or seasons. That story just follows those very specific parts of Jon Snow dealing with the white walkers and those very specific parts of Danni mastering her dragons. In that narrow slice, one person's discovering the problem in the north, the other is coming up with the solution in the east, they come together, have sex, and then kill some ice zombies (I'm being facetious about the RS here, but it just seemed so feebly done in season 7 I couldn't resist.)
So you could have a "title" storyform (for want of a better term). It just wouldn't in any way encapsulate the actual series which is about these fractured kingdoms coming together. From the standpoint of the Jon/Danni thing, all those other stories are just part of the background context (i.e. they make it harder for them to solve the overall problem of the ice zombies).
My resistance to looking at it through this lens is that it kind of renders the series itself shallow – turning the thing Martin was aiming for (a rich, complex, highly nuanced examination of a long war through multiple intersecting characters and arcs) into the exact thing he was trying to avoid (boy hero gets magic sword + hot, frequently half-dressed girl with dragons and slays evil dark lord).
It's an excellent question – and one I'm unlikely to be able to answer. Having written a completed series of about 650,000 words (for context, Lord of the Rings is about 450K and Harry Potter is just over 1 Million), I can tell you that the least important thing for me at any time was the overall series arc. At any given moment, a novelist, screenwriter, director, or pretty much everyone else in the entertainment business is concerned with whether this next book/film/game is going to be a success. For me that means leaving everything out on the field every single time. I just couldn't afford to be counting on book 3 being the exciting bit while book 2 would be the slower bit.
A second consideration is that, regardless of where you intended to go, its where each instalment takes you that defines what happens next. Sometimes small things, like a subtle change in the relationship between two characters, completely negates the virtue of what you intended to write next.
With that in mind, Dramatica's been very helpful to me in writing a series in two ways:
- By forcing me to see thematic holes in my draft.
This is kind of the most obvious use of the model because when you're trying to make the book the best it can be, identifying what's missing is crucial. Frequently I'll find I've got an IC and an RS but that they're so overlapping as to be indistinguishable from one another. That forces me to give the IC a true throughline, and to give the RS a reason to exist (rather than just the "We'd like to see a romance in there somewhere" notion).
- By helping me to avoid repeating the same storyform
Often when I'm working on a sequel, I'll go back and re-map the book that's published as a Dramatica storyform. Seeing what I've just done abstracted into Dramatica variations and elements makes it easier for me to push the new book into a different storyform – and thus keep things fresh.
So for me, it's less about Dramatica giving me a structure for a series and more about Dramatica giving me tools to think about each book as I'm going and how to make each one compelling in its own right. In this sense, I'm going for completeness (i.e. exploring all four possible concerns in each domain over the series) rather than progression (i.e. having it tell me what each book should do.)
Not sure if that's helpful, but that's kind of where I'm at.