I ... don't find fic that impactful, tbh. I don't think there's been a propub book that's left a mark on my thoughts on writing or my aspirations, either.
*scrolls through bookmarks*
The closest thing would be In Fire 200k+ of Anakin Skywalker character study and redemption arc set in a Silent Hill fusion. It was nice and ambitious and very, very good at what it did. Also, the author had 3 different endings planned, based on the game's endings, and kept a running tally of "points" each ending got based on keywords in the comments, writing the next installment towards the ending with the highest point total at that moment. Not something I'd ever do, but very cool nonetheless!