I've been saying for years that Dany's story is antagonistic and that Sansa will win everything. She's the pawn that slowly crosses the chess board to become a queen. To the extent that there still are rulers in Westeros when everything is said and done (I don't think for a second that there will still be an iron throne), Sansa will be the one people turn to. My hopes for the last season are extentions of those two ideas, so I was fairly happy with the way the first episode of season 8 turned out.
I think Dany's darker shades have been a clear and consistent line throughout the story. I reread the books last year and rewatched the show two months ago, and it's even more revealing with the benefit of hindsight. Dany to me is a character who starts out with good but misguided intentions and deeply questionable morals (she knows exactly what the dothraki are in the first book, and while she watches them rape and kill a woman she thinks, with tears in her eyes, that this is the price one must pay for the iron throne and willingly accepts it going forward), and then gradually becomes consumed by power. She's Martin's best achievement in my opinion; not because I think she's a brilliant character (Sansa is always going to be my favourite) but because the transition from protagonist to antagonist has been so well done that many people still make excuses for her power hungry, warmongering ways.
Martin, a staunch pacifist who refused to serve in Vietnam, has likened her dragons to nukes, and talked at length about how power is subtle, and just because Dany has the power to conquer and destroy doesn't mean that she has the power to rebuild or reform. Her failure in Mereen illustrates that point: she fails to replace a slave-based economy with a viable alternative and then gets tired of politics and compromises and leaves for Westeros, leaving a literal cutthroat in charge. Dany speaks to Tyrion about "breaking the wheel", and at the time it seems like a hint about a more democratic reform for Westeros. In retrospect it's clear that what she meant was that she'll make sure there are no other contenders for the throne however.
Her arc is an oncoming tragedy, and anyone who thinks she's going to sit on the iron throne is in for a hard awakening. Her birthright was never valid after the rebellion that dethroned her father, and even if it were she was never the first in line of succession. Jon's parentage has been the story's worst kept secret since day one, and it's not a coincidence that the show has Sam throwing that spanner into the machinery in the first episode of the last season. Maybe Dany would have backed off once, very early on, upon hearing that Jon had a better claim. She's way past that point now though. She wants to rule because she can, because dragons and armies give her the power to seize thrones and titles through fire and blood.
There were hints last season that she'll have a fallout with Missandei and Grey Worm too, and I think it's going to bring up another aspect that the story has had to address for several years now but has mostly shunned away from: Dany replacing the slave masters at the top. When she 'frees' the unsullied not a single person out of eight thousand defects, and it's pretty obvious why. They have no families, and they're all castrated so they can't start ones. They have no gold or possessions. They have no skills other than war, and they live in a country where slavery is still at large and no one wants to pay former slaves anyway for services they got for free. Are men really free when there's no other choice presented to them but to march on? Davos and Jon ask Missandei whether she's truly free or in name only, and while she seems sure that she is, the story would not have brought it up unless it was about to test the boundaries of that freedom.
The same thing happens when Dany frees Mereen: she stands up and speaks in front of people who have no notion of what freedom even is, and they rush to show their affection for a new, kinder master. The white saviour image of a bleached, highborne woman in a fancy dress crowdsurfing an ocean of brown people with slave collars is amazing. Just amazing. And her fans are eating it up. Stuff like this is why it's so difficult not to be deeply impressed by Martin as a writer, mediocre stylist as he is. Dany doesn't understand slaves, because her own slavery was a forced marriage to a war king, not servitude without any human rights. She wants to kill one of the Sons of the Harpy, but after Ser Barristan schools her on the kind of justice her father, The Mad King, doled out, she shows restraint and insists on a trial. But when one of the former slaves who is now her advisor misinterprets her indecisiveness as her wanting the man's head but her hands being tied, and ends up killing him for her, Dany has him beheaded in front of all the other slaves in the city. It's her worst instincts as a ruler at play: She starts out wanting to punish the masters but ends up executing a slave instead who takes revenge the same way she did when she nailed 160 slave owners to crosses along the road to Mereen. It's a confusing moral lesson for anyone, but most of all people who have never known laws and rights in their lives, and they begin to turn on her.
The key point is that she doesn't learn anything from this; instead she doubles down on her absolutism. When she arrives in Westeros she shows up with Drogon and the dothraki and wipes out an entire army (burning a year's worth of food in the process for visual effect because she doesn't understand the long winters of the country she's invading and has never lived in - a point that is sure to be addressed again as people begin starving in the north due to the arrival of her army). She then burns the Tarlys alive as prisoners of war because they wouldn't bend the knee to her. Tyrion and Varys are aghast; Varys compares her to his service under Aerys when the latter used to burn dissidents with wildfire. A small act of mercy would have prevented setting Sam, the show's de facto moral conscience, firmly against her. But Dany fails these character tests precisely because she's unfit to rule and reform. She's only fit to conquer, and it has become her sole purpose for wanting the iron throne at this point. She has no supporters in Westeros, no claim to the throne, and no connection to the country having never lived there. Vital plot elements keep aligning against her, and she's set up for a big falling out with everyone she once counted as allies.
