There's no escaping shades of reality in any SF/Fantasy I've ever read. Scratch at any of them, and huge problems are revealed.
McCaffrey's dragons are too powerful. Large size, flying, and fire breathing is pretty stock stuff for dragons. But her dragons are also telepathic, and so emo they each bond with a chosen human rider so closely they kill themselves if their rider dies, and they can teleport (mere flying just ain't good enough), and worst of all, time travel. I'm guessing she realized she'd gone too far, but couldn't make any acknowledgment. Instead, she tried to paper over the problems by introducing restrictions and limitations that unfortunately come across as too arbitrary.
An integral and needless law of Tolkien's world serves only to make things needlessly more special and their loss more tragic. It's this notion that great things can only be done once. Why can't Yavanna simply grow more trees to light the world? Why did she quit at 2 trees to start with? Why can't Feanor make more Silmarillions? No explanation is offered, we're simply told that's the way things are. There's enough real misery in the world, there's no need to invent reasons to be even more miserable. But some people, especially story tellers, do that to be more dramatic, more poignant. This desire for specialness also infects authors' thinking on copyright. Even apart from the obvious self-interested reasons, they're predisposed to like copyright, like the way it puts art on a pedestal.
Another problem with many fantasy stories is what I call the Godzilla or King Kong problem. Huge scary powerful solo monsters that no one expected certainly are dramatic. But improbable. Monster movies are inherently ridiculous because even if such a monster appeared, it would have no chance whatsoever of doing much damage before the massed might of millions of people brought it down. The Watcher in the Water at the west entrance to Moria would in all likelihood starve very quickly. One need only wait. If, somehow, the monster is magically sustained, there are all sorts of other things a crew of engineering sorts like dwarves could do to solve the problem it created. For one, could open another exit nearby, but out of its quite limited reach. Or, could probably set off a rock avalanche, crushing anything in the pool as well as displacing all the water with debris. Could also undermine the dam and drain the pool that way. Or perhaps a more low key approach might work, like dumping poison in the pool. To prevail against all the things a crew of determined engineers could try, the monster would need extraordinary abilities by the dozen. Even the Balrog should have a very difficult time prevailing against an entire nation of dwarves. The Balrog only ran them out of Moria. The sandworms of Dune are slightly more plausible, but still not a real problem for a civilization that can travel interplanetary space. Only Sauron went as far as setting up a rival empire, and thereby stood a real chance of prevailing.
Middle Earth follows many rules of nature. The land is for the most part geologically plausible and sound, with mountains in ranges, rivers rising in the mountains and flowing downhill to the oceans, and woods, marshes, grasslands, deserts and ice in places one might expect. Despite the prominent place of magic in the typical fantasy story, its impact is really quite limited. Gandalf used his brains as much or more than his wizardry. Since the land is familiar to so many readers, why not model its climate for fun?