I listened to the episode of MBMBAM the other day where they interviewed Patrick Rothfuss, and he had an interesting comment on a question about where to start with worldbuilding for a fantasy book or D&D campaign. He pointed out that in J. R. R. Tolkien's books, he barely develops the magic system at all. Gandalf's powers as a wizard are left completely vague, and in comparison to an author like Rothfuss himself or someone like N. K. Jemisin, there's basically zero discussion of the physics or science behind “magic” in Middle Earth. Admittedly I'm not much of a fan of Tolkein, but from what I have read of his work, to even say he has a magic system would be an overstatement, although he does use magic.
But of course he clearly has put hours upon hours of effort into geography, history, wars, and linguistics in his books—because those are the topics that interest him and what he is, in Rothfuss' words, “a nerd for”. And as we all know, his enthusiasm and devotion to those topics comes through in his works and as a result they're excellent (or at least enjoyable to some people who are nerds for similar things!). Nobody would read Tolkien and come away from it saying “Wow, he really didn't do much work on his magic system, did he?!”
(By contrast, Rothfuss' books have, in his own words, an emphasis on “hard sciences”, currency, and economics, because those are his interests. And while Jemisin's worlds are very rich in many domains, a lot of her worldbuilding focuses on axes of oppression, essentially.)
I've always thought of myself as not much of a worldbuild-er type of author, but Rothfuss' comments made me rethink that. The novel I'm currently working on, Valentile's Knife, doesn't have a hugely fleshed out world and isn't what I would have previously thought of as a masterpiece of worldbuilding. But like... I'm a nerd about psychology, sociology, queerness, and disability, and all of those interests come out in the worldbuilding I did (and am doing) for this novel.
The geography of the world is vague (and only fleshed out locally); I faked linguistics with neural nets (which turned out to be much more fun and intellectually stimulating than conlanging would have been!), and I haven't given more than a passing thought to commerce and economics. These are all (well, besides economics) aspects of worldbuilding I've forced myself into in the past. I have only ever abandoned one novel since I started finishing novels, and that was one I pushed myself to worldbuild really hard in ways that were not interesting to me. There were other mistakes made with that one, but a big chunk of it was that when I planned it, I created a big, complicated, fleshed-out world for the main character to run around in, that had basically nothing I actually found interesting in it. The main character was to spend 95% of the novel physically separated from his lover and everyone else he had an intimate relationship with.
This was a disaster. Ultimately the thing I'm the most a nerd about is intimate relationships. I'm a lonely, queer, affection-seeking autistic with attachment issues and relationship-related trauma (and don't I make myself sound like a fun time! I also like long walks on the beach!), so of course I'm fascinated by topics like queerness, abuse, psychology, disability, and how all these affect our most intimate romantic and familial relationships. I like linguistics, and I can muster up a passing interest in geography, but I don't make time in my day for those things the way I do for those other topics. That novel started out lifeless, did not improve over the course of the first 30 or 40k words I wrote of it, and ended up abandoned.
By contrast, the novel that first made me kind of sit up and say “I think I actually have something here” was one where most of the worldbuilding revolved around gender and disability—and their effect on the relationship between two autistic(-coded, it was Fantasy Autism) main characters.
My latest WIP, Valentile's Knife, which I'm very excited about, is narrowly focused on the relationship between Valentile and Gilleashar, who are together and interacting throughout nearly the entire book. Almost all of the worldbuilding grows out of examining that one relationship, and this has produced probably the richest and most interesting setting (to me, of course) I've ever written in. The social interactions and intimate relationships in Valentile's Knife revolve around an idiosyncratic hierarchical system of division within families, and there are worldbuilding details related to the structure of the “nuclear” family across different cultures, who has children and when, etc. There's a lot of meaning embedded in who knows sign language, who uses it, and when. Gender and sex are both wildly different in Calonheil and Almeredh than in the familiar world, and this has meaningful and complex ramifications for the characters as well.
I didn't think of this as worldbuilding at first because a lot of it directly pertains to sex and romance and the interpersonal side of things. I barely think of it as worldbuilding because it feels like an extension of character building: I'm creating a framework building out from pre-existing characters to enrich and support the relationships they have with each other, and to give myself a space to play with them and, you know, make 'em kiss.
But it is worldbuilding. Not only is it worldbuilding, but it's worldbuilding I'm very excited about and motivated by! And I think it's intellectual and nuanced worldbuilding despite the romantic, interpersonal, “mushy” bent of it all. Maybe not in quite the same way as the worldbuilding of, e.g., Hannu Rajaniemi, but still.
Basically what I'm saying here is: It's time we owned up to the fact that whatever genius invented the ABO AU is on Tolkien's level, and we all just have to deal with that.