Top graph shows the number of English language fanworks posted per month in the Faraway Wanderers (novel) and Word of Honor (tv show) fandom tags on AO3 as a percentage of all AO3 works posted in the same period. Bottom graph shows the raw numbers. I used AO3′s work search to grab counts while logged in.
I wanted to check when the English-language fandom for the novel vs. the show took off, fanfic-wise, but it looks like they took off at the same time, March 2021. The tv show started airing February 22, 2021. As it happens, the fan translation of the novel wasn’t completed until a few weeks later, March 14, 2021. So, this is speculation on my part, but I’m guessing most people found the novel because of the show, and the few English speakers who read the novel before the show started didn’t want to write fanfic until the translation was complete(?). The novel is by Priest, so Guardian fans and other cnovel fans would theoretically be interested in reading it, but apparently not to the extent of writing fanfic. (??)
The AO3 tag situation is quite different from the MDZS/Untamed fandom, where the start of English fanwork posting makes it look like the English speaking fandom got into the novel because of the cartoon, and the fan translation was completed before the live-action show aired. On AO3 it looks like a lot of show fans decided to use the book fandom tag (because everyone else was using it? as a substitute for a meta tag that the wranglers refused to create?), so now the MDZS tag has more fanworks than the Untamed tag. I’ve seen a lot of complaints that most of them are show-canon fics. Out of 41K MDZS fics in English, 25K are also tagged with The Untamed.
Whereas the Word of Honor tag is more than 4x larger than the Faraway Wanderers tag. Although the Faraway Wanderers tag may suffer from the same problem as the MDZS book tag: 849 out of 1050 are also tagged with Word of Honor. Unless these are really book fics that want to be seen by the show audience?