But they managed. The contortions of logic they're forcing the characters through for the sake of plot are painful.
Sansa suggested the soldiers need time to rest and recuperate. She was entirely correct. They're going to have to march at least a thousand miles from Winterfell and be ready to fight when they arrive. Not to mention the dragons. If Rhaegal had had more time to let his wing heal maybe he could have dodged those ballista bolts. The urgency was entirely manufactured. There was nothing to be lost by waiting, even for months or years. Daenerys dismissed lords and politics as unimportant - "Only the throne matters." Um, no it doesn't. Ask any of the many kings who were deposed and executed because they lost the support of their lords. Cersei is so weak that she literally doesn't have a land army any more and has had to employ mercenaries, that is how little support she has. Any half-decent PR campaign could have painted Daenerys as a conquering saviour, a legend out of stories, flying in on dragonback to save the kingdom from the terrible forces of darkness. Lords and what armies are left in Westeros would have been tripping over themselves to swear fealty.
Only the need to wrap up the story in two more episodes is pushing an attack on KL now.
I don't think that's entirely fair. Most inhabitants of Kings Landing are ordinary uneducated smallfolk who don't have the ability to pack up their lives and move elsewhere. They are as innocent as anyone and they don't deserve to die. If Cersei showed any signs of being a half-decent ruler and queen the cost might be too high. But Cersei is an egotistical murderous tyrant who has already surpassed Aerys the Mad in body count and whose main ally is Euron, leader of the Ironborn, parasites who survive off rape and plunder. She needs to go. There will be a terrible human cost to it but it's the morally correct course of action nonetheless.
However there has been no examination of any other options except (i) nuke KL, or (ii) surrender. They have a skilled assassin who can literally disguise herself as anyone and who would be more than happy to introduce Cersei to the pointy end. Did anyone even ask her? They have Varys, who knows all the secret tunnels and passageways in KL and the Red Keep. They have Davos, who knows the waters around KL well enough to sail them undetected in the dark. And they have Bran, who apparently knows everything everywhere because the show never bothered putting limits on his abilities.
There is no proof. The word of a crippled boy is not going to be believed by anyone outside of Winterfell and a single piece of paper is a flimsy thread to hang a claim on. The most obvious proof is that Jon can ride a dragon; I would have liked the show to run with that, had people be astonished and awed and Varys with a poleaxed look of shock realisation on his face. But no.
Even then, a Jon-Daenerys marriage is a stupidly obvious solution to nearly everyone's problems. With R+L=J (yet) not common knowledge it would be natural to enter it with Daenerys as Queen and Jon her prince-consort. He wouldn't argue. He's already sworn to follow her. Sansa wants the North to have autonomy? Jon can name her Warden of the North and the Starks will forever have a strong voice in the realm. From Daenerys' perspective a potential rival is turned into a permanent ally and will not sire children who may later become threats to her reign.
(Though the lack of of heirs will be a problem later on - I have seen no evidence that Mirri Maz Duur's warning to Daenerys was untrue and I don't imagine weeks as a corpse has improved Jon's fertility either. But that's always been an interesting blind spot of Daenerys', who believes herself barren yet unhesitatingly pursues a throne that will inevitably be lost again upon her death.)
Claiming Daenerys would "Bend [Jon] to her will" is both (i) ridiculous and (ii) untrue. Jon and Daenerys have had several significant disagreements in the time they've known each other. Some of those times he has compromised, in some of them she has. The last time I checked that was how a healthy marriage is supposed to function. Not one ruling absolutely over the other. Daenerys is extremely strong-willed; that's the reason she's a queen now and not a barbarian horse-lord's sex toy. But she's not too stubborn to listen to advice - she actively seeks it out and often takes it even when she disagrees.
In fact the Jon-Daenerys marriage is so obvious that the show couldn't have the characters themselves discuss it because they wouldn't have been able to come up with any convincing arguments not to, and instead we had that ridiculous scene between Tyrion and Varys. Not that either of them have a single braincell left between them at this point. If the marriage debate scene was bad, the attempt at parley between Daenerys and Cersei was absurd.
Tyrion knows Cersei better than anyone except perhaps Jaime. So I can't imagine why he thought appealing to her better nature or love for a child she hasn't even borne yet would achieve anything whatsoever. Cersei is a bitter, vengeful, spiteful, vicious, amoral, power-hungry tyrant with questionable grip on reality. In S02 Blackwater she was sitting on the Iron Throne - with the son she loved - ready to poison them both, ready to die, rather than flee or be dragged off the Throne. That was before she lost her children, her father, her brother-lover, endured weeks of capitvity and was driven naked through the streets of Kings Landing. They would have more chance of persuading Stannis Baratheon to give up and open a butterfly sanctuary on Naath. I can forgive Daenerys for not quite having a handle on Cersei's character yet, but from Tyrion it was unforgiveable.
The writers seem determined to 'subvert expectations' aka make stupid plot twists for shock value. I wonder will they shock us by having Cersei win. Considering the incompetence displayed by her enemies she almost deserves to.
