How do we know this isn't the very first ballista ever invented in Westeros? Have they been seen before on the show or mentioned in the books? It's quite possible that they simply had no ranged weapon strong enough to pierce a dragons' scales/skull until we saw Qyburn's demonstration. You act as though GoT is expected to have identical technology as we did during the medieval era, yet they have stuff we didn't and perhaps vice versa.
You mean how do you know. I know because I know the lore.
Maybe the demonstration was to stop them shitting themselves by pretending it'll work. Morale etc.
Big daddy dragon had magic scales when he was alive, and you'd probably never get the chance to fire at the dragons as a stationary target on the battlefield, certainly not at a controlled range. Kinda like the 'longbow' tests that fire at point-blank range at a flat piece of tinfoil and conclude they can pierce any plate from any range.
I'm just saying against baby dragons as a one-off, I would believe a lucky ballista shot at decently close range could take one down. At least that wouldn't be as much of a cop-out as a character nobody ever heard of turning up out of nowhere and gunning down the ultimate dragon with a black arrow (I'm looking at you Tolkein).
You'd expect the scales to play a big part yes, but then the demonstration would be literally pointless. But the fact it pierced the skull was the centerpiece of that whole scene. It wasn't just for morale simply because of how TV works. You don't make a scene like that if if the intent is for a character within a story to convince another character within a story that something is true. It was meant to convince the viewers, which the composition made very clear.
The dragons that were young but just old enough to be ridden, in the lore, were all killed by other dragons, save for one or two whose deaths weren't detailed. There is an account of a scorpio hitting one dragon in the eye with a lucky shot (the lore says "lucky", not my addition) which killed it. But you don't call something the secret weapon against dragons if you need a lucky shot and it's been done once in history, and you're fighting three dragons.
The point is this: because they've presented this weapon as the answer to the dragon problem, you can rest assured we'll see it work against Daenerys' dragons. It working is believable in the setting, if you get very lucky, but it being presented as the answer is not. The characters are treating it as "well, that's the dragon problem solved, there" kind of thing.
IF they employ dozens of those things it'll be better, as it becomes more believable one bolt gets through. But it still wouldn't make sense given the setting's history with dragons and conquests.
Still a lot better than the Hobbit, of course.
