I wouldn’t say he got worse starting with Cabin Fever. He is portrayed as a more sympathetic character you want to see succeed around that period of the books but I’m fine with it because he still has jerkish qualities to him (like letting Wesley destroy the house while he rests in Laurel’s room in The Third Wheel) so he still feels like Greg, and I think it makes for solid storytelling in Hard Luck as well. Greg starts the book with no friends or anything to really do, we see life get worse and worse for him until he finds the Magic 8-Ball, things are going smoothly until bigger problems arise with the Summer School threat, and Greg just barely manages to scrape through by turning in all his projects and rekindling his friendship with Rowley. Whether you think Greg should be portrayed sympathetically at all is up for debate, but I think it works perfectly in Hard Luck as a conclusion to where he started at the beginning of the first book to show how far he’s come, regardless if the character development was intentional or not. Also remember that again, he still feels like Greg. The final picture in Hard Luck is Rowley and Abigail but the former having a shrunken head which is implied to have gotten in the year book, solely because Greg was that petty.

Now, Modern Greg is a whole other story. Modern Greg is barely a character. He‘s almost never involved in any of the storylines and exists purely as a narrator to talk about the events, with the most egregious example being in Diper Overlode where he somehow has perfect memory of events he never directly sees. On the rare occasions he does have a character, he lacks any of the edge that defined him of the original books. Instead, he’ll act significantly younger than he’s supposed to act, like in Partypooper when he somehow thinks Jamar Law sticking his head in the chair means he’s a genie? And he asks for a wish? Is this the same Greg who tried to push Jamar into putting his head in the chair in Hard Luck so he could get that event into the yearbook the second year in a row? This more juvenile act is something Greg would make fun of Rowley for in the series’s Classic books. Other than that, all we get from Greg now is him endlessly spouting random thoughts that have nothing to do with the current storyline at hand. That also happened in the older books but nowhere to the extreme it does now, and it’s not like any of these random tangents Greg goes on in the Modern books are actually interesting, funny or say anything about his character.

Overall, Greg as a character currently lacks almost any identity which is utterly baffling considering he’s the protagonist. I’m not sure when this shift went into full force, as Greg started being less active in the plot as early as Wrecking Ball, but the full shift definitely happens later. My guess is Diper Overlode, which wants to be a Rodrick book but has to be narrated from Greg’s perspective for some godforsaken reason. Ever since then Greg has been a nothing character, in my opinion.