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No way; Usopp all the way. Zoro may have improved but it's only one step. He's learned to cut through steel. That's it. New techniques, sure, but who's to say he JUST now learned them, and aren't they just basically variations of his other attacks? Exception being that swordless thing he did in the Groggy Monsters fight. But Usopp...every single thing about him has improved dramatically. His fighting strategies...his weapons-making abilities...even his lies have improved! No one ever believed anything he ever said, but Mr. 5 fell for it when he lied and said he fired a gunpowder star when it was really a hot chili pepper star! Not to mention his repertoire of personal weapons (fake 5-ton hammer), along with Nami's tact...he saved Nami's life with that thing, she would have died without his help. And he has definetely shown bravery above and beyond all else in taking on Monkey D. Luffy, a guy who can take down a Shichibukai, a Logia thunder-god, and every pirate captain on the high seas he meets, singelehandedly. It's not just about sword abilities, it's about all-around improvement. Zoro started off as good as he always was; I mean, look how easily he took out all of the Whiskey Peak agenst on his own. Usopp had to work hard to survive Mr. 4's bat to the face, and everything else he had to go through. He's not an extraordinary person with extraordinary strength like the big four of Luffy, Zoro, Sanji and Chopper, which makes his improvement vastly more notable. At least that's what I think. Zoro's is too one-dimensional, Usopp's is universal.

Luffy has continually gotten stronger and stronger. Zoro is as well, but I dunno I haven't seen him much surpassing anyone really but wait perhaps Luffy would be more unstoppable if he learned some strategy as opposed to constantly punching people everywhere. Nami hasn't done much but hey from when you first met her compared to after Arlong, she has gotten better. Robin, I can't say since I've stopped right after the Crocodile fight. Sanji has improved in... cooking? Like that would ever even matter if anything <.< Ussop though has become more brave very slowly its hard to remember him the way he once was. Chopper is uhm just the same as when you first met him. If you wanna say that Chopper grew by becoming more trusting, go look at Nami's adjustment.

Chopper, he use to be shy and hastle, now hes the opposite

Actually, he still got owned if you think about it

Compare it with the other battles where Luffy had to try. They were much longer than his battle with Ussopp. Even if he had to try, Ussopp's endurance can't really compare seriously with the others. He's a resourceful runner with a huge arsenal of tricky weapons. Everything lies in his mind and tools. Of course he'll be owned by Luffy when it comes to strength cause his tools don't have the punch required to take out Luffy. And now that Luffy has Gears, Ussopp can't even touch him.

He didn't say Zoro was one-dimensional, he said that Zoro's IMPROVEMENT was one-dimensional.

And I've got to say USOPP USOPP USOPP. He went from completely useless to an actual contender.

Luffy. Hes grown not only physically stronger, but wiser. Cmon a guy who can figure out that by pumping more air to his leg he can increase his blood pressure to make him stronger, has to be a pretty dam smart guy.