I agree with pretty much everything else you said, but I'm afraid that's nothing but headcanon. The showrunners have made it clear that Daenerys decided to burn the city while perched on the walls, after she had burnt the fleet, the walls, and the golden company with zero civilian casualties, after the city had surrender. I'm not gonna quote pendel again, the post is right above. But I am going to quote D.B. Weiss, from the behind the scenes segment after episode 5.
"I don't think she decided ahead of time that she was going to do what she did. And then she sees the Red Keep, which is to her the home that her family built when they first came over to this country 300 years ago. It's in that moment, on the walls of King's Landing, where she's looking at that symbol of everything that was taken from her, when she makes the decision to - to make this personal."