I will use your post as a template and this post is not only addressed to you.
We do not know enough about the Others in the book to know exactly what are Martin's intentions towards them. All we know is that in the distant past, they tried to obliterate humanity (and the living) and that humans, giants and children of the forest has defeated but not destroyed them and that they built a magical wall of ice to keep them at bay. We know nothing about their culture, their motivations or if even they have motivations. All we know is that they are a lethal threat to humanity.
Yeah, that's generaly how things work.Characters who should have died did not die (presumably because they are needed later in the show).
No. The Night King was killed in 82 minutes. The whole point of the Battle of Winterfell was to goad him to attack Bran and kill him.The one who was built up over several seasons as being powerful and the biggest threat to all in Westeros was killed in about 20 seconds.
The Night King was very powerful and shown to be so several times during the series. He can create White Walkers. He can raise the dead easily (Hardhome). He can interact with Bran when he's tree-worging and can even mark him physically. He can detect Bran when he's worging crows and unworg him. He can one-shot a dragon in flight by throwing a javelin. He can raise the dragon to undeath. He's impervious to fire, even dragon fire. However, he has on Achille's Heal: as every other White Walkers, he can be killed if he's hit with obsidian or valyrian steel weapons.[...]we learned that he was not as powerful as he was thought to be,
But first, you must get to him. And that part has been hard as hell.
Indeed. Just like Sauron would have been history if Isildur just threw the damned ring in the fiery chasm. I don't see any problem with that.that someone could have killed him thousands of years ago,
And that's where we may address the "Arya had nothing to do with the NK" argument. Yes, I'll admit that I would have prefered if Jon had been the one to kill the Night King. However, I disagree that, first, Arya had nothing to do with the Night King and, second, that it is bad writing if she did.For example, Ned's death fit into the overall coherence of the narrative up to that point and while some if not many disliked his death, it made sense. The way the NK died did not.
Arya had some reasons to want to kill the Night King. First, the obvious one: he was attacking her brother in her home. Arya is all about "the Pack". Second, since the very first season, Arya's theme has been death, just like her favorite "brother", Jon Snow. From Syrio Forel ("There is only one god, and his name is Death. And what do we say to Death? Not today.") to the Faceless Men who are worshipping death itself. And let's not forget her little prayer. Then you have Bran that gives him the valyrian steel dagger, the perfect assassin's weapon. And then you have a plan which amounts to an assassination plot. The army will hold off the dead, while Bran is used as bait to lure the Night King who will then be killed. Arya is a trained assassin. It made sense for her to be there. She should have been there since the beginning to be frank, and that's a problem. So, maybe the NK's plot gets diminished (maybe), but Arya's own character arc gets more meaning and impact.
True, Jon would have been better, because he does have more links to the Night King. However, that does not mean that he had to be the one who killed the Night King. Let's look at Lord of the Rings. What were Eowyn's links with the Witch King? There was none. If the Witch King had to be killed by someone who had serious motives to kill him, it would have been Aragorn. Afterall, he's probably a Numenorian, like Aragorn, and he destroyed the northern kingdoms ruled by Aragorn's ancestors when he was King of Angmar. But no, he was killed by a lady from Rohan with the help of a hobbit with a numenorian blade. And it was done rather quickly too.
And Sauron? Was there a big confrontation between Aragorn and Sauron? No. Like the Night King, Sauron used his troops to protect him. All it took to destroy him, was that someone threw his ring into Mount Doom. And it was not even Frodo who did it, but Gollum. And as soon as the Ring was destroyed, Sauron died and all his empire fell into dust with him in mere seconds. Sounds familiar?
That's the one part I can agree with. I would have prefered if they ended the show with that plot. It's more a matter of "when" than "how" for me. That being said, the war for the Iron Throne and its family feuds has been the main plot for most of the show and the main concern for most of the characters. Therefore, it has a greater emotional impact than the WW's plot and could end the show on a higher note.So the NK and the dead are essentially a glorified subplot.