Regarding Bocchi the Rock I have to disagree, all I want is more of that show beamed straight into my eyeballs!
I can't think of any anime that could be improved with less episodes, because I only continue watching something if I actually like it, and I can't remember anything I just walked away from. Maybe one of the two versions of Fullmetal Alchemist? That show really didn't impress me much at the time though, really only watched as much of it as I did because friends were so into it at the time.
Non-anime wise, Dexter, Weeds and Supernatural all should've ended wayyy earlier and were kept in life support because of prior successful ratings, off the top of my head.