About realism and unrealistic in fantasy and fantasy films/books:
Every good fantasy book takes place in a fantasy world, and every good fantasy world has its own laws. These laws must be relatively logical, conceivable and logically non-contradictory. Thus, in a good fantasy world, there will never be an all-destroying sword and all-reflective shield unless it is said in advance how they will interact with each other. And the better the fantasy world is worked out, the more you can talk about the logic and illogicity of the specific action in it.
The world of "Lord of the Rings" is a well-designed fantasy world. And if somewhere in Tolkien is said about the increased heat resistance of dwarfs - then let's swim in the wagons for gold (only the wagon will most likely need to be crushed, but this is already physicists will tell), if there is nothing about it, then it is worth considering it an additional fiction of the scriptwriters, with what the true lovers will remain dissatisfied.

By the way, the same Harry Potter world is extremely contradictory and illogical even in the original.