I partially disagree, and think GRRM (and the TV show) mostly paint morally ambiguous characters with some redeeming qualities and some grievous flaws.
> Sansa, Sam, Davos, Jon, Arya, Tyrion, Brianne, Bran, Robin, Yara
Of these, I consider only Sam, Davos and Brienne to be "clear good guys". Jon arguably comes last. You missed Eddard, the one truly moral character that gets killed because of this (I think this was GRRM effectively showing that moral good guys will get killed if they cannot be a little devious). Let me explain why the others aren't, in my opinion:
- Sansa is portrayed almost as stupidly naive. From the beginning she buys into all sort of courtly things that -- even if true -- were pretty shallow. And they turned out to be untrue. When she finally wakes up to the harsh realities, later in the show, she becomes manipulative and cold. She's on the right side, sure, but you can easily see her turning into another Cersei, given the chance. So she's either painfully stupid or dangerously vindictive.
- Arya joins a death cult and becomes callous. She's driven by hatred and vengeance. Again, you could easily see her turning into an assassin for hire. You already mentioned her psychotic outbursts.
- Tyrion... well, there's a lovable but definitely morally gray character. No need to explain further, I'm surprised you included him as a clear-cut "good" guy. Maybe because he's the only likable Lannister and stole the TV show.
- Bran starts as likable and gradually turns into an enigmatic, unempathetic, alien creature. Who knows what he's thinking, he certainly won't tell. Some fans speculated (incorrectly, it turns out) he was going to turn into a Big Bad mastermind by the end of the show. Even if this was incorrect, it shows the character was not perceived as unarguably "good".
- Robin. Is this the teenage lord of the Eyrie, the one who still was sucking from his mother's breast, was very capricious, easily manipulated, and eager to let prisoners "fly" out of the Moon door? This was a very creepy character, not a good guy.
- Yara. An amoral pirate, willing to kill or be killed for power. It just happened that she didn't truly hate her brother and that her relatives were even worse.
Re: the bad guys. I mostly agree with your list except (Euron Greyjoy in particular was an irritating charicature, and they didn't even bother with the Night's King), but for two exceptions:
- Cersei. It's true she's the main villain -- other than the walkers -- of the latter seasons, but she's nuanced. She's obviously suffered. She's driven mad by grief and power lust, but she's also a woman in a world of men. She refuses to become simply the concubine of a powerful lord, or a mother. And she's truly capable of love, though the objects of her affections are sometimes misplaced (and she's quick to hate as well). I think there are admirable traits in Cersei's character, not enough to overlook she's also a mad, self-destructive murderess, but enough to consider she has her shades of gray.
- Daenerys is mostly the good gal until she suddenly turns mad. You don't get to ignore she was good for most of the series, so you cannot place her in the "clear bad guys" box.
Re: gray characters. Yes, Jame, Bron, Varys. Most in the small court in Kingslanding. Most of the nobles. Most of the soldiers, be it free men or slaves. I don't you can claim most weren't gray, when the whole show is populated mostly by morally gray characters!
The final episodes of the final season are not the whole show. If they were, you could claim Cersei is mostly a dead woman in GoT, just because she dies in the final chapter.