All those armies and all those brilliant fighters and all of Bran’s foresight weren’t enough. In the end Arya basically wins the whole war all on her own with a plan she came up with all on her own (after receiving a hint from Melisandre). We have no on-screen indication that the Night King was weakened from his battle against Jon and Dany, nor do we have any indication that the only reason Arya could pull off this move is because of the battle she was just taking part in.
If our heroes had watched Episode 3 ahead of time it seems as though their best plan would legitimately have been to send the Dothraki south, stuff as many people into the crypts as possible (well-armed) and leave the gates of Winterfell wide open with Bran in the Godswood. Then tell Arya to hide in the Godswood (like she presumably did in Episode 3 after her chat with Mel) and ambush the Night King when he arrived to kill Bran. It would have been the exact same outcome, but that thousands of people would still be alive.
And the result is that the show's big theme of humanity working together ‘we all have to put aside our distrust and fight together against the army of the dead’ is completely undermined.
Bran did not take this dagger when given a chance earlier in the season, so maybe he foresaw it, and maybe it was his plan after all.
https://mashable.com/article/game-of-thrones-arya-valyrian-dagger-night-king-explained/
So there is that and sorry to bust your theory.
Not sure how that matters? Even accepting your premise, it would mean that Bran formulated a plan on his own, which he did not relate to anybody else, and Arya, formulating a plan on her own without telling anybody else, was able to kill the NK because of the dagger Bran gave her.
So all of that other stuff just feels like much ado about nothing. It created the illusion of an epic story but for the most part it didn't go anywhere, at least as far as the Night King plotline was concerned.
Really, you could have had a show that entirely focused on their journeys to reach that moment with the Night King and you would have had all the information and emotional resonance you needed, because they were the only ones who had anything to do with defeating him. And of course hardly anybody of significance was even killed by the Night King, so there wasn't actually much of a point to all the build up in Episode 2 about how they were all anticipating their potential demise.
I think that's why I keep coming back to how the end of "The Long Night" felt like something from a Marvel movie to me. Because it caused so much that came before it seem as though it were part of a story about a single heroic person with superpowers, instead of the struggle of an entire civilization comprised of disparate factions led by flawed leaders to come together to thwart an existential threat.