How strong are dragon scales realistically?

The realism of dragon scales changes from media to media, legend to legend.
Sadly, dragons are scientifically impossible. Even a tyranosaurus brought to life would be too hard pressed to find enough food to survive without a population of dinosaurs to prey upon.
As most dragons fly, growing powerful armored scales would weigh them down terribly making them expend even more energy flying, requiring a stronger skeleton to support those armored scales, stronger muscles and bigger wings to carry that extra weight, and then require even more energy and wing span and muscles to fly with that extra weight, and so on and so on into a riddiculous spiralling feedback loop.
The bottom line is that a flying Dragon doesn’t exist unless the ugly thing is powered Soley by magic, thus doesn’t need chemical energy and traditional physics to fly, and thus has no need for food.
But what about a grounded dragon with scales?
So, it’s certainly possible for nature to create an animal with armored scales. It has done so repeatedly. It is thus possible for nature to possibly make a creature with hardened scales, backed with a subdermis like kevlar, backed by squishy layers of blubber to reduce bludgeoning impact.
But the question is why would nature bother?
That kind of armor would require the most incredible expediture of energy to make over a creature’s lifespan and for what reason would it need such potent defenses? Elephants are the king of the Savanah and don’t need anything beyond thick skin. Elephant seals and walruses do very well against polar bears with just blubber, which is itself insulation against cold and energy stores.
More over, most mega-fauna predators kill their prey by knocking them down and choking them to death, rather than clawing their skin. Armored scales aren’t going to prevent that, but they will help weigh the creature down so that if it did get knocked down it would be harder to get back up.
Finally, if the dragon breathes fire, then armored scales might get in the way of reflecting and radiating heat energy. A dragon might accidentally cook itself alive with its own firey breath and the blazes it starts around them. Fire breath is such a potent weapon that a creature that evolved such an ability wouldn’t need armored scales, or even need to be big at all; it could be a small creature evolved to digest carbonized animal and vegetable matter and hibernate between meals. The fire does its work for it: No armor needed, nor claws nor speed no flight.
So, even a land based draconic creature isn’t likely to have super armored scales, even if it wasn’t the apex predator it’s environment.

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