Oh come on, the Straw hats ARE strong - it's just that it's hard to fight without air to breathe! They're not Enel or Frieza, you know
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Luffy could grab CC in his elemental form and would be wiping the floor with him if the guy wasn't smart enough to remove all the air around the Straw Hats. Come to think of it, the exact same think happened with Zoro on Fishman Island - if he wasn't underwater, he would've cut Hody thirty times over even if he used all his damn pills
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