1. The Least Pirates being the least threatening villain group in the entire manga.
2. Usopp, Brook, and Chopper not getting fights even though Oda could’ve very easily had them fight P1, WsW, and Perospero
3. Half of the Scabbards being filler. Ashura and Kawa didn’t need to exist. Their roles and backstories could’ve been condensed into Denjiro’s character. Have Denjiro be the former gang leader from Kuri who joined Oden after losing to him in a fight. Cut out the filler of having Kawamatsu watch over Hiyori for a few years. Just have Denjiro be her protector from the beginning. Also, Kyoshiro being the one who had the blueprints to Onigashima would make much more sense than Ashura somehow obtaining them. Kiku was totally useless and only existed because Oda wanted to draw a trans samurai. Raizo was also totally worthless. Just have Kanjuro be the ninja of the group (his drawing ability is already basically ninjutsu anyways). Having Kanjuro be the one that the Dukes were protecting at Zou would make his betrayal sting even more. Kin’emon, Denjiro, Kanjuro, and the Dukes were the only Scabbards who actually had an important role in the story. Izo’s cool though, so I didn’t mind his inclusion besides not doing anything that important.
4. Big Mom being a retard and forgetting she has ACoC while fighting Kid and Law. Just give Kid ACoA and Law ACoO if they need to be stronger to beat a BM who actually uses ACoC. Idk why Luffy and Zoro are the only new gen characters that Oda will allow to have any impressive Haki feats
5. None of the weaker SHs unlocking Haki. They’re a Yonko crew now, yet 6 of their 10 core members can’t even use basic Haki? Franky, Robin, and Nami honestly didn’t deserve to beat their F6 opponents without unlocking Haki
Honorable mentions: The Nidai Kitetsu being totally useless, Zoro never visiting Ryuma’s grave, no Poneglyph lore dumps (despite Robin having access to the two extra ones from WCI, the Ponelyph in the Shogun’s palace, and the Poneglyph in Onigashima), Drake, Apoo, and Hawkins being borderline irrelevant, and the Numbers being totally irrelevant