How much of Star Trek is extrapolative? There are sooo many issues from how teleporters or shields work to half-Vulcans. But like most space based sci-fi things like FTL drives and artificial gravity are just assumed. If not warp drive or n-space or some other excuse then stable worm-holes left by "an ancient civilization" or similar tropes. People go to another planet and can eat the plants and animals to gain nutrition while simultaneously not dying from some virus or bacteria that we would have no resistance to whatsoever.
There is some sci-fi that is more grounded, as well as some fantasy. But the stories we write are still, for the most part, centered around individuals. Those individuals are exceptional, whether because they are just normal individuals thrust into extraordinary situations and rise to the occasion or because they are enhanced somehow.
Related back to D&D, I try to think out the logical consequences of what our world would be like if magic and monsters were real. We can extrapolate how would the supernatural change the world just as much as we can extrapolate how advanced technology can change the world. I don't see that much of a difference.
Well, I just think you're wrong about this. Let's look at Star Trek. Although far from hard sci-fi, it still has used its platform to explore issues of how humanity would interact with alien species, the implications of artificial intelligence, whether emotion or reason-based decision making is superior...I could go on and on. Plenty of Star Trek episodes are extrapolative.
Fantasy just doesn't tend to do that. Fantasy comes from romance, tales of knights on supernatural quests, and from (more interestingly, IMO) foundational myths. Although both genres can feature heroic, idealized characters, fantasy has a tendency to present characters that are "chosen one" type figures in the Arthurian (or Jesus) mode. And fantasy looks backwards for inspiration, to quasi-medieval settings with kings and queens.
There are some writers who use fantasy to explore interesting themes. In a novel like
Tigana, Guy Gabriel Kay subverts the trope of the Dark Lord by humanizing the villain and telling half the story from his perspective.
Game of Thrones is still backwards looking but combines fantasy tropes with historical inspiration to explore the darker sides of human motivations and ambitions. But both those authors are consciously working
against standard fantasy tropes, to some extent.
As a genre, sci-fi allows the scope for authors to take chances. I had to think hard to come up with examples of fantasy novels that challenged my preconceptions. I could give you a list a mile long of science fiction novels. As I wrote earlier, challenging our preconceptions is at the heart of science-fiction; it's sci-fi's original
raison d'être. That is just not the case for fantasy as a genre. It is an overwhelmingly safe genre, full of benevolent kings and righteous causes.
Fantasy at its most powerful focuses on those hero's journey tropes, on the common myths and aspirations of humanity. That's what Tolkien does so well; that's what George Lucas does too. I would argue that Westerns tend to fall into this category as well. I argue that science fiction is more naturally aligned with horror, as a genre that aims to subvert and unsettle. That's why I think the difference between science fiction and fantasy is foundational.
I don't like power-gaming precisely because it feels like that kind of Patrick Rothfuss-style fantasy where the protagonist is a prodigy at everything. I just don't enjoy that. I think that only works if it is executed by a talent in the league of Tolkien, who is work at the level of myth. But I can't get any kind of relatable or interesting characters from that. I enjoy the trappings of fantasy, but I want the characters to be believable, imperfect, and just trying to do their best. That's why I won't touch alignments with a ten foot pole - I think the whole concept is fantasy morality on steroids. That's why I hate when players start from "what would be an optimal character" and insist that they start with "what is an interesting want, need, and flaw?"