So zombie mountain has been nothing but a robot taking instruction from Cersei and Qyburn. At not point in the previous episodes do we see any indication that he has any sense of autonomy or self awareness. There's been no flashes of nostalgia or thought or action towards his previous life.

The Hound shows up, and suddenly he has a perception of being? Enough to disregard orders, kill Qyburn and start fighting his brother? I don't buy it.

One thing the books emphasize that's kinda been lost on the show, is how much of absolute savage the mountain is. It is said that Gregor Clegane raped Rhaegar's wife before killing her, and smashed baby Targaryen against a wall to kill it. He allegedly killed his father and sister to get his inheritance early, and has multiple wives who've died suspiciously. This is a man who was using rats in a bucket to kill men in Harrenhal. Why would he feel any passion or remembrance towards his brother?? Him scarring him is just another footnote in the long list of fucked up things the mountain has done, and I don't see it as enough of a motivation for him to overcome his Frankenstein's monster reality.

Even more importantly though, this series is a series of subverting tropes. Yes, on tv and in the movies the heroic figure is allowed to get his comeuppance against the ones who have wronged him, but that's not real life. Real life is get unfairly bullied as a kid, and the bully goes on to live a successful and happy life. Real life is being head over heels in love with someone, only for them to break your heart in the most fucked up way possible. Like sometimes, often even, there's no justice for doing wrong. There's none! Donald Trump been scamming people for decades, and he's president!! I don't want to see the mountain get killed by the hound, I want to see the hound going to the Red Keep, and get burnt alive by Drogon. I want to see him be so overcome by nerves and emotion he drinks himself into a stupor and misses the entire sack of King's Landing. Something other than what happened smh.

As much as I love the hound, dying a heroic death, with the city falling and a dragonfire beautifully flaring in the background is soooo fucking boring and cliched. Sometimes a bit of fanservice is nice, but in this case it was a bad move.

(and don't even get me started on Sandor's redemptive character development showing him turning away from his Hound persona. This post would be twice as long loll)