I don't think any plan would have been "good" against the NK. Typical defense plans, like holing up in the castle, are worthless against an enemy that doesn't care about losses and will mound themselves up to get in. Even with some of the best fighters on the walls, they were overwhelmed. On top of that, they didn't have enough time to prepare the defenses, which limited even more delaying the inevitable as the wights just went right over it. I do agree, though, that the battle was somewhat dumb as they didn't use their artillery well at the beginning (use it to light up the night and see what the hell is out there at least) nor did they use their archers to rain dragonglass on the initial surge.
Also, after Hardhome, I don't think the White Walkers were dumb enough to be anywhere near the front line until the end of the battles as they knew that the humans have weapons that can kill them. The WW at Hardhome was surprised when he was hit, but the rest were observing what happened.
Anyways, off to the next episode. Is Cersei's storyline supposed to represent the fake Aegon storyline in the book? It seems odd that the Golden Company would be bankrolled by the Iron Bank of Bravos whenever there are supposed to be connections between the Iron Bank and the Faceless Men, who seemingly sought out Arya.