Death Note is a popular answer, and I also agree that its ideal stopping point is…
Death Note
L’s death
Bocchi the Rock is another show that I felt would be at its best if it stopped at episode eight. If the upcoming compilation movie stops there, I may consider it superior to the TV series. It’s not unheard-of. Violet Evergarden’s film-length recap stopped at Episode 10.
I want to see more of Bocchi-chan's rock!
The title drop + roll credits is its peak and climax. I hoped its finale would be amazing. However, episode eight overshadowed episode 12. Everything after E8 felt like a lede for an S2.
What are yours?
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.
I can’t complain on more Bocchi content. It’s the presentation that I’m wondering in retrospect. I wonder how would it be like if Bocchi S1 ended in episode eight and the rest becomes something like “Bocchi -piece-” Horimiya style.