NK was always going to die in single combat with an opponent welding a Vsteel blade or he was going to actually win. I have no issue with one of the top killers in the realm having that honor.
I do agree that the whole "Winter is Coming" for 7 seasons for it to be wrapped up 3 eps in is lame AF. From Ep1 Scene 1 the Walkers WERE the threat, their quick dispatching is a disservice to the lore. Personally they should have gotten fucked hard at WF, had to retreat south with a band 1k deep, Meet with an envoy of KL to say, "Hey, umm so that whole AotD thing, Yeh they won, we are ALL thats left of the north", Then the south bands together and fights the big fight.