Realism can mean different things to different people, and some people seem to think it doesn’t matter at all in science fiction and fantasy. Especially fantasy since the definition of the genre requires things that aren’t possible in reality.
But then there are just as many who insist on the opposite, and think everything in fiction has to have a basis in reality. Even though I have “magic” with a “scientific” explanation in my own work, I don’t agree with this.
No, the way I see it is this. Explicit fantasy elements are just that; explicitly unrealistic. But everything else in the story, things that actually exist in real life, should still be held to realism. For example, Superman can be strong enough to lift a plane with one hand; but the plane shouldn’t be strong enough to support it’s entire weight on an area the size of a hand.