Go look back at previous seasons. Dany has spoken about burning cities for a long time.
Also did you notice the Ravens flying around the Red Keep? Reminds her of Varys betrayal.
I think she sees the Red Keep and Kings Landing as “The Wheel”. In her mind as long as it’s intact and the people keep believing in tyrants then she hasn’t done her job. But in the process does she also become a tyrant? Maybe not in her mind.
Those closest to her from the beginning who were basically her moral compass and trying to guide her (Mormont, Missandei. Varys...) are all dead now.
With Arya, it took someone more vengeful than her to convince her not to continue on a suicide mission. Cersei was going to die anyway. Arya has more to life for than The Hound and he helped her realize that.
Again both plot points happened way too quick without much build up.....another episode of Dany spiraling and questioning what to do and Arya traveling with The Hound going over their motivations would have worked better.
Really. Who cares. It’s all in good fun.
The best parts of the show were the duels and battles anyway. The Mountain and The Viper was cool.
Alan