I’ll go first: Romance is extremely overrated. I am far down on the aroace spectrum where I feel no attraction, so I don’t really understand the point of romance fics. I’ve read a few that were good, but I usually avoid them unless it’s something I really want to read. I exclusively write gen except for one crackfic I made. No hate to authors of romance fics, I just find them boring and overdone.
Late, but, as a big enjoyer of Self-insert fics, I don’t mind they follow the standard isekai format and don’t go overboard with changing the world. Sure, some change is good and characters should be alterred due to the space an SI fills, but letting the overarching plot flow is a great boon for fanfic authors.
Fanfic is about enjoying and, forgive the wording, messing around with established lore and setpieces. Kind of like how gaming has the modding community, the literature community has fanfics who choose to spice up or manipulate existing stuff. You don’t have to necessarily go on and completely overhaul or make full-on novel tier total conversions if you get what I mean.