What narrative is this lol
Fishman Island: Had his own fight, the blood transfusion
Punk Hazard: Saved Mocha's life
Dressrosa: N/A
Zou: Saved the Mink tribe, his TS medical skills were highlighted when fixing up Zunisha's leg
Whole Cake Island: Led the way in securing the Mirror World, which allowed the Straw Hats to do as they pleased during the first half of the arc
The only arc I'd really hold against him is Punk Hazard, but honestly, what do you expect, it's the arc where we first got a good look at Law, and there's no way Chopper was gonna overshadow someone like Law given Oda's plans for him. Even so, that's a point of being underwhelming, the word you're looking for, not useless.
I don't know what made it look like Zou would be his time to shine, but it was a short arc where no major fights happened, so being disappointed is odd. Hell, it's weird to even single out Chopper here, when he actually did the most relevant action out of the entire crew that arc.
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Got me out here defending Chopper's underwhelming ass, shame on y'all