There are some crazy choices here. I'm not sure I'd call any of the anime listed here perfect, but Death Note? Really? A show which people generally agree falls off after the first half?
TBH I suspect Frieren is going to have that same issue unfortunately. Reading the manga has given me a strong impression that the author has no idea what they're writing and is just coming up with it as they go. I don't expect Season 3 to be as well-received as 1 & 2 were. Honestly I think a show boasting an incomplete story should be disqualified from lists like this anyways. How can you say something is perfect if you haven't seen large parts of it yet, and those parts may never even exist?
Nippon Sangoku had incredible art, and incredibly one-dimensional characters. Maybe this author found its political storyline fascinating; I'd say if you want that you'd be better-off watching Legend of the Galactic Heroes.
Even most One Piece fans will admit the anime has horrible pacing at times.
I could probably go on, but I'll refrain.