Game of Thrones co-showrunner David Benioff talks about that scene in episode 5 (Eastwatch) of season 7 in which Daenerys decides to burn Randyll & Dickon Tarly alive after they refused to bend the knee:
“One of the things Dany has found immensely frustrating in beginnings of this war against Cersei is that she is being asked to fight on a certain moral standard and.. Cersei isn’t. Because of that, Cersei has an advantage over her. The more ruthless opponent will often win. I wouldn’t say she is acting like the Mad King because it’s rational. She’s given them a choice and they choose not to bend the knee to her and she accepts that choice and she does exactly what she told them she would do. And from her standpoint, she’s not acting insane in any way. She’s just being tough, which is what she needs to be to win. That’s one perspective. Tyrion has a different perspective and hopefully people watching will have their own and they’ll decide whether they think what she did was just or immoral.”
Check out more in the video below.