Jon marrying Danerys would have made him complicit in everything she's done - including roasting Samwell's family alive. It's not the incest that ooks him out, it's that she's a psychopath. She's a convenient psychopath when they need her armies but once her armies are a liability he's done with it. She would have had him murdered eventually anyway - she's rejected everyone she's ever loved because they get in the way of her power and double-crossed her way out of every threat. The balance with Jamie and Cersei is perfect: Jamie surrenders to love over duty while Jon chooses duty over love. That's why he was never going to end up with Brienne - he's not banging his sister because he can't find another girl, he's banging his sister because what matters to him more than anything else in the world is banging his sister.

The only people who ever gave a shit about the White Walkers were the Northmen. The only people who had any sense of the White Walkers were the Northmen. For everyone else, The Wall was like Australia - a convenient place to shunt people so you don't have to execute them. Therefore, the only time anyone really rallied behind the North was when it could be demonstrated beyond a reasonable doubt that they would bring about the end of Westeros. Really, Bran is order and the Night King is entropy; Bran had to employ strategy across the timeline in order to defeat the Night King, who basically marched guilelessly across the landscape.

The Battle of Agincourt took a day. The English were outnumbered somewhere between 2 and 6 to 1. They took a couple hundred casualties max and slaughtered something like ten thousand Frenchmen.