So something like The Magus by John Fowles you would write off as it has a fantastical aspect, or Robertson Davies. I started reading so called Adult books when I was 7 or 8.
There is a huge difference between YA and childrens books. YA these days is as dark as it comes.....I look at it as could the book appeal to teens ....usually by way of a character who they can relate to.
Jemisin has that character big time....maybe even two if you consider the one stone eater.
Hunger Games and other very dark dystopian fiction includes characters and adventures that appeal to teens but also read widely by adults.
I'm surprised you like Scifi at all as most are as unrealistic as any witch and wizardry fantasy. David Brin's uplift series for instance or the entire
Vorkosigan Saga by Bujold.....even legendary ones like The Foundation requires a huge suspension of disbelief.
You certainly did not sample the best of Mielville at all. I found he was experimenting with the
City and the City and did not quite pull it off tho it was "interesting" and the guy can write.
If you really want a wordsmith ...Guy Gavriel Kaye is simply astonishing.
Jemisin is as out there as it comes and you may not like it at all.
I rarely consider ANY science fiction as serious fiction....speculative fiction yes and some very well written but not serious fiction.
The English Patient, almost anything by Fowles, The Alexandria Quartet, The Lighthouse, Jude the Obscure , The Reivers. (almost anything by Faulkner )....those are all serious fiction but junk like Catcher in the Rye and anything by Tom Wolfe just tripe.
Maybe A Canticle for Leibowitz is one sci-fi that fits to serious fiction, it's almost as far out as Jemisin. 1984 perhaps as well and Huxley's Brave New World, Anathem might turn out classic.
Reading the review on the Revengers it certainly is space opera and has a YA appeal but not a children's book by any stretch.
https://www.barnesandnoble.com/blog/sci ... ter-space/