...by writing off the entirety of King's Landing and remarking that all they care about is severed heads yet suspiciously not wanting anyone's severed head for the Sept blowing up with two of KL's most beloved people in it?
I don't know why they thought this was a good idea. Just show the population terrified about Cersei, praying to the seven in secret and being worried about a foreign invader army, done, it would've took 3 minutes to stablish something that makes sense.
For instance the way Cersei convinced the Lords to fight for her was great, and most importantly it *makes sense*, it fits this world, Dany is indeed the daughter of the mad King and has an army of people known to be rapists and pillagers.