I think, in the rush to criticize the writing, people are missing a really critical fact; it’s a systemic problem with the show and I’m not sure that even the best writers in the world could fix it:
The Army of the Dead is really fucking boring.
Oh, it can be cool when it’s used for one-off horror episodes (Hardhome, The Door) or in brief scenes where it’s mostly serving to color the main events. But the show was inevitably going to have to bring the Dead around to be the central antagonists, and in that capacity, they’re sorely lacking. They have no interesting motivation. They have no dialogue. Unlike every prior antagonist, they don’t fight among themselves or jockey for position, or fall in love or make jokes. They don’t even have personality traits, other than “implacable.”
I’m just not sure there’s a compelling way to write ten coherent hours of television about a battle with such things. It’s like writing a story about fighting a rock, or a tornado, or a flood. Sure, the pure action can sustain you for a few hours, but once you get beyond that there’s just no story anymore.
What should “really” happen on Game of Thrones is everybody, everywhere should drop everything and fight the Dead until they’re gone. Arya and Sansa should be like: holy shit, ice zombies, maybe we can wait to hash out our childhood drama and Cersei should be like holy shit, ice zombies, maybe I should change my facial expression for the first time in six years and Euron should be like holy shit, ice zombies, I won’t burn any boats until those are taken care of. But then there would be absolutely no story to tell, beyond a series of battles against faceless ciphers that can’t end until the show does.
So they have to invent these ridiculous ways for the human conflicts that actually provide story beats to continue. And again, I think that’s an essential problem with the overall structure of the story, and the fact that they put it off as long as they did is actually pretty impressive.