This was really interesting to read (your post, I mean; I haven't read the book). The debate about fanfic writers going pro so often focuses on the ways that a) the techniques used in fanfic are similar to original fic's foundations and thus fanfic makes for a useful training ground or b) the techniques used in fanfic are fundamentally different from original fic's, and therefore inferior. So it's really interesting to think of original fic like this intentionally leaning into fanfic techniques w/o the serial numbers filed off—deliberately integrating them into original fic rather than trying to cover the fannish tracks.