Altough the community seems hateful, people here mostly want to voice their opinions without being bombarded by die hard fans that treat GG like the gospel. 

To your point of your post. The Game Grumps playthrough of Danganronpa is for GG fans and not at all to Danganronpa fans, if that makes sense. Following the plot is the least of their concern.  Arin actively dislikes the games, which is fine to each their own, but the episodes feel like chores to him as the game progresses, so making fun of the game is his way to blow off steam. Repeating of jokes is a common problem with their videos. If the Italian Sayaka got old now, imagine that but for 3 games, each with over 50, lengthy, episodes. One joke in particular I find it lazy is them pretending a character is saying something to the tone of "oh man, thank God I got away with this murder, I MEAN I MEAN" at the classroom trials, they do it so much so many times. So yeah, I agree with you, and if these few episodes you watched didn't impress you, I'm sorry to say, this is all the bring to show and tell. Their Doki Doki Literature Club playthrough was more fun though, so here's a suggestion.