Fantasy vs. Science Fiction

Okay, if a dragon's hide reflects magic, energy, bullets, projectiles, doesn't get wet in the rain, and protects from heat and cold, then, I repeat, why is the dragon killed by some pathetic knight with a simple sword in his hand?
And don't tell me that he was just bragging in a tavern to impress the waitress.

It's definitely not metallic or diamond.

Why is that? There's no basis for it.

Because otherwise, they wouldn't be able to move, let alone fly, because there's no aerodynamics, no feathers to keep them in the air, and their body mass is around ten tons. And don't start saying something like "their magic keeps them in the air," because that would be completely stupid.

I'm going to burst your bubble, but Dragons are cold-blooded creatures.

But since they move, and quite actively, they emit heat. That's how it is with reptiles;)
Besides, they have a furnace in their belly to breathe fire.

A blaster is just a charged beam of energy) it will slip through and won't reflect like a laser)

If you insist on that, imagine the blaster hitting a pumpkin, causing injuries to the poor lizard's head. And if it doesn't hit, it ignites the air, which quickly burns out, and the dragon has nothing to breathe. Or the fire penetrates the lungs and esophagus. I doubt that if a dragon breathes air normally, the furnace is not a separate organ, which means inhaling hot air is, let's say, unpleasant.

Some Dragons can cast teleportation;)
And by the way, it's not a fact that they are slower.

Some Inquisitors can perform Exterminatus.

and it's a fact that they are slower. Don't forget how much effort it takes for a ship to fly just to overcome the planet's gravity, and what overloads it endures. Now, remember how fast dragons fly in games and movies, for example, in your beloved Eragon. I doubt they are even faster than a military helicopter.

It would be a great sight, a huge ship chasing a dragon. Awesome!! X_X

Nonsense, a huge ship will just aim its guns, and the dragon will try to escape them if it's not stupid.

...in the end, the long-suffering Smaug was killed by a single arrow that hit its belly. There is no super-imba scale on their belly.

Added 2 minutes ago
P.S. A laser will reflect off a good, smooth, clean mirror without causing any damage, because it is nothing more than a directed beam of light.

Added 1 minute ago
P.P.S. Dragons' skin is absolutely not mirror-like; at most, it can have a shine in sunlight, but that's it.