I'm not a Dramatica expert by any means nor do I dismiss other practically-focused story development models, so I can't speak with authority on either your concerns about the fundamental workings of Dramatica or on how much it parallels other theoretical approaches to understanding story. What I can offer you are two thoughts that occur to me on a frequent basis both with using Dramatica in my own work and when reading the folks on this discussion board:
The first is that there's no discussion whether socratic, didactic, or otherwise that's going to convince someone that Dramatica is or isn't a complete (even within its own claims of the Grand Argument Story) model of storytelling. Why? Partly because the experts here (and it's fair to call them experts given the years they've put into understanding and working with the model) have already had this discussion dozens if not hundreds of times and, I think, are less than enthused about debating it yet one more time.
The other part, though--the part I care about and would draw your attention to--is that Dramatica's usefulness (or lack thereof) is not contingent on how convincing the explanation around it is. It's usefulness is dictated by whether or not it enables, inspires, or otherwise facilitates you to write a better story.
This brings me to my second point:
I make my living writing novels and one consequence of that is that I'm forever meeting other writers who are struggling to break out--to get a publisher for their books or just get more readers. Any writer with a basic grasp of the craft can put together a story without Dramatica or any other tool or model. Any kid who's watched a movie or read a comic book can come up with a model of storytelling and, with some work, write a story. There's a basic level of Western storytelling that we all inherit and with a few tools, I honestly believe any literate person willing to put in the work can write a novel or a screenplay.
The thing is, once you get past the basics or writing, you hit the wall, and the wall is not about having a tool or model tell you what to write next. The wall is how do you make your story just 5% better.
That 5% may not sound like much but it's often the difference between an 'okay' book or screenplay and a 'great' book or screenplay. Once you've gotten the basics down, the struggle--every single day--is to get just 5% better, because in that 5% is the difference between the people whose work gets published, bought, and loved, versus those whose work sits in a drawer.
If tomorrow someone came out with absolute conclusive evidence that Dramatica was absolutely correct or absolutely false it would make no real difference to me because my stake is not in the theoretical. The only question I ask myself when I'm bashing around in Dramatica--struggling with the god-damned difference between obligation, responsibility, commitment, and whatever the hell other element that sounds distinctly like a synonym to me--is whether this is helping me make my story 5% better.
In my case, it does. When I sit there trying to figure out how and why "The Present" means something different to my book than "How Things Are Changing", I'm forced to think deeper about what's going on in the story and this sets the mechanics of my brain working. It's from that tension--between what Dramatica is saying (whether I fully understand it or not) and what I know about my story--that I focus my creativity to come up with a better scene, character, or arc. It's from that process that I get my next improvement, my next 5%, and that is worth more to me than if Calliope herself, Greek Muse of Epic Poetry, were to descend from Olympus to tell me which is the one true model of storytelling.
Let critics and literary theorists become lost in the often semantic debates about the essential structure of stories. As writers, our only concern is finding tools that make our own writing better.