I would probably say it's less of a series wide deconstruction, and more the topic of this particular arc. You're right that it's had hints before, but this arc has very much thrust it into focus, but I think most of the arcs have focused on de- and re-constructing concepts that are well trodden. Like Bailong broke down the exam/tournament arc concept and reconstructed it by playing it sincerely in the end, reminiscent of other classic takes on it.
I do know that going forward from this arc, D's concept of what it means to see the world and his allies in it will have been completely changed, as shown by him starting to reject the idea of "Invader" as a spectacle, rather than his previous ideas which always leaned more into the cartoonish. Which is what Chidori challenged him on during their fight - what are you really fighting for, and what are you really about?
I am unsure if this is just an arc or a conclusion.
Unless magic takes place, the story which was being told prior can no longer resume, as most of the characters are dead.
And every subplot which has
concluded in this arc has followed a fairly specific formula. [Person] identifies with a specific archetype or character, and the pursuit of
becoming that character and realizing that narrative in their own life ultimately results in their undoing.
Ukyo identified with "the truth seeking journalist," and found her own destruction. The Yellow JFC identified with "the hero of justice," and found her own destruction. The list goes on. Everyone who has died committed themselves to a specific role or fantasy, tried to inhabit something other than who they actually were, and the consequence of this was the death of the self - literally and/or figuratively.
So one has to wonder, what shall be the ultimate fate of Sakurama, who has committed himself to the role of hero, and whose commitment to high minded ideals has left him scarred, maimed, and his sister dead. What about D, who has committed himself to the role of villain and conqueror? How about Suzukiri, who loved her departed family dearly, and whose hatred for the "heroes" who killed them twisted her into identifying with villains.
I also think it's significant that Yellow has survived
because he is an amoral monster who doesn't identify
at all with his role as a hero. Hisui, likewise, has survived
despite just being herself. She hasn't committed herself to some sort of role or act. She hates invaders, so she kills them, and is ready to die for it. She likes D, so against her principles, she chooses to look the other way. I question whether she'll make it out of this alive, but at least up until now, she's survived a bunch of near misses.
Basically, I think this constitutes a (foreshadowed) narrative transformation. All of this is about the endings of characters - where their commitment to narrative roles leads them. Perhaps they'd still be alive if they just tried to be themselves, like Hisui or Yellow. So I would say this is series wide, since the narrative was leading up to here, and really has nowhere else to go - unless Negi pulls another jarring transition, the thematic content of this arc feels like the natural conclusion. Even if I still think it feels too dense and rushed.
