I'm glad you asked:
1. THE Wall is made of solid ice, not stone, for one.
https://gameofthrones.fandom.com/wiki/The_Wall And "for two", that was an undead dragon, which had a different sort of fire that the books haven't really tackled yet. But like the showrunners have continually done, they took significant liberties to just push through the wall rather than having the horn mentioned in the books come into play
2. In the history of Harrenhall, we learn that the stone cracked and melted from the dragon fire, it didn't just erupt in a Michael Bay-esque explosion meant only to serve a cinematic purpose
https://awoiaf.westeros.org/index.php/Burning_of_Harrenhal
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The showrunners have perverted just about everything that made this show great. Jaimie Lannister went from a cocky villain to a reformed man who found honor and chose a different path. Then we're to just accept at the last second the sister he abandoned he suddenly wishes to return to and he just decides he's going to throw away the entire redemption arc that has spanned multiple seasons to do so. Gimme a break, that is absolutely piss-poor writing and a slap in the face for GOT fans who actually paid attention to character development
Dany going mad-queen I get, although the speed at which she descends into madness was way too fast to make much sense. She goes from a champion of freeing the oppressed to becoming an out-of-control psychopath.
Tyrion Lannister, the voice of reason and logic just decides he's going to have faith in this blatantly changing and darker Dany and turn in Varys (not to mention how the hell did Dany even find out before Tyrion spilled?)
The Hound suddenly forgets he's afraid of fire as the dragon lays it down above him and the city burns all around him?
The Lanister soldiers are like stormtroopers in this battle while everyone in Dany's army is like a jedi, mowing down 8 of them at a time and that's supposed to be believable? I think the Lannister soldiers killed under a handful of their attackers while they were all just slaughtered like fish in a barrel, putting up barely any resistance.
Dany carpet bombing an entire fleet and city prepared with Scorpions to fend off her one dragon (suddenly the massive fleet seems to only have one scorpion on it, on the lead ship, and no one else is firing, and the magical aim they had in their ambush in the previous episode has disappeared and they can't hit squat now) completely flies in the face of what they wanted us to believe in the previous episode the Scorpions were capable of. They went from overpowered to completely useless (and massively unused) just for the sheer cinematic spectacle of it.
The whole series has devolved into a mindless foray into showcasing what the showrunners believe to be "cool" moments, and has thrown out any semblance of maintaining continuity with the characters and storylines that have brought us to this point. It's like they threw the entire history of the show in the trash and said "nah, forget everything you watched previously, we're just going to do it this way cuz itz kool!"
The Faith Militant in this thread defending this absolute shit-show is maddening