"At various points in the show, Daenerys is ruthless in dealing with her enemies. But she never gratuitously slaughters innocent civilians until this point. It just doesn't make sense for her to start doing so when she has already won."
They say there were signs of that, but than we could assume that Jon will kill everyone in the next episode, because he did chop a head just because someone refused an order, and he did hang a little kid. she did not have to kill all the people she did (previous this episode) but she did what everybody that had power did, only she did not chop heads or hang people, she had dragons.
And by doing what she did, she did not get here revenge in the sense of someone bloodthirsty of it. she did not kill Cersei she does even know is she is dead.
In the last 15 minutes i was cheering for arya to do some kind of ninja shit and just kill here. i would believe it even if she jumped from the wall on the dragon.
"But the showrunners' explanation at the end of the show suggests this is not the case, but rather that Daenerys just made a sudden decision to "make it personal" by destroying the Red Keep."
did not seen it but even if she wanted to make it personal, maybe as a person from non english place i don't understand word personal. this was everything but personal.