Fantasy vs. Science Fiction

An AK can penetrate stone. And not just an AK. Armor-piercing bullets can penetrate tank armor, so what's the problem with stone or dragon scales?
Dragon scales are most likely similar to stone in their properties. They are definitely not metallic or diamond-like.
One fighter jet would be enough to kill at least a few dragons.
The idea that dragon scales reflect energy is completely unfounded and far-fetched, only to make dragons seem even more powerful and invulnerable.

You're also saying that Arcat's dragons aren't fire-breathing? Are they fire elementals?

They are fire elementals.