Daenrys doing all of this i'm pretty sure it was GRRM idea's from the beginning. If Daenerys path to madness was better explained and not rushed in 2 or 3 eps it would've been fantastic.
Daenerys just feels like she has lost everything and everyone is against her. She resent Westeros in the end. She had to flee as a baby to the other side of the sea hiding from murderes for years until her brother decided to sell her as a slave. She then started to feel she deserved to be the queen because she was the mother of dragons. She lost her true love Drogo in the process. She fought from nothing to gather an army that conquered cities and free people from their opressors. People loved her for that. No one give her nothing for free and she had to make strong decisions everytime. Just before going to Westeros she was told by everyone of her assesors she was going to be the perfect queen in Westeros and everyone would love her there too.
And then, she comes to Westeros and everything starts to go south. Tyrion and Varys suddenly do not trust her decissions anymore, but she still does what they told her to do. Westerosi people don't respect her nor see her as the true Queen as she was told from childhood. Then Jon appears, she ends loving him and she is willing to do everything for him. So when he asks her to help him defeating the white walkers she gaves her full sopport to the cause. She ends losing one of her dragons and in the battle of winterfell she loses his most loyal friend and a lot of her beloved soldiers. She made a huge sacrifice for the people of Westeros. By the end of the battle no one in the north or the westerosi side thanks her or apreciate her efforts. In fact they still try to undermine their power once is revelaed Jon is a Targaryen. Then she loses another dragon and her best friend at the hands of Cersei and her allies, and she still is despised by the same people. After that Daenerys is betrayed by anyone from Westeros she trusts: Varys, Tyrion, Jon, the North allies, Jaime, .... By this time she's being surrounded by jealous, traitors and incompetent people who give her bad advise after bad advice, and even Jon seems to not love her anymore. She doesn't understand either why the people of King's Landing is not fighting for their freedom like the people in Meeren did. Why they do not revolt against Cersei. Do they prefer Cersei as queen she must wonder? She realises she doesn't understand these lands and their people as much as she believed and that Westeros will never understand her either.
So here we are, in last episode. The battle starts and ends soon with a total victory. Everything seems fine. Tyrion asked her to stop the attack once the bells ring. The bells are ringing and then she sees the Red Keep, a Targaryen symbol from her ancestors. The same people who build this city. A city that give their back to support the people that killed her family years ago. The same people who did not fight against that usurper of a queen called Cersei. These people were living in a city that was built by Targaryens and they did not respected that at all. Nobody loved her here. At this moment, she hates the people of King's Landing as much as Cersei. All of them are culprits. All of them need to learn a lesson. So, if Westeros people do not want to love her, then they are going to fear her. That's her decision, and she starts to burn everything.
I'm pretty sure the main ideas behind all of this, are the same as GRRM. The problem in all of this, is that all this process from 7th and 8th season probably should have been a lot more episodes. It seems to me like eps 1-3 and 4-6 could've been complete seasons. It would have helped build the characters progressions of Daenerys, Jon, Tyrion, Varys, ... a lot better. The way the show did it, seemed like characters were doing stupid things or 180º turns just so the story went to the way the writers wanted. It felt rushed, and this is all on D&D fault. This show deserved better...