In One Piece, there are numerous characters who can unleash abilities that defy expectations. Nonetheless, in a world where unimaginable feats such as summoning meteors can be actualized, the Straw Hats have always retained a rigid ordering of the top three. This can be seen any time Luffy's crew battles an opponent. During these skirmishes, Zoro has consistently fought the second-strongest opponent after Luffy, while Sanji takes on the third-strongest adversary.
However, although this well-established order has remained unchanged since Sanji joined the Straw Hats, the future of One Piece is not set in stone. In this case, the devil may lie in the details, as the untapped potential that Sanji possesses may eventually enable him to stand out as a powerhouse among the Straw Hats, topping even Zoro in terms of raw strength.
Sanji Has an Incredible Range of Powers
Since the beginning of One Piece, all the Straw Hats have been increasing in power and gaining new abilities. However, unlike the other Straw Hats, a lot of Sanji's new abilities complement rather than displace previous ones. Eventually, his potent mix of abilities could culminate in devastatingly powerful power stacking. Sanji is physically fast, strong, capable of enduring large amounts of damage and has an endless amount of stamina. Since Sanji first put on his raid suit during the "World Cake Island" arc, he has slowly unlocked latent powers. These powers include enhanced healing regeneration, increased muscle mass and a fortified exoskeleton. During future fights, these abilities could easily provide Sanji with a trump card. The combination of enhanced regeneration and a durable exoskeleton, combined with Sanji's high stamina, is an overpowered, potentially broken combination.
This contrasts with Zoro, who, while incredibly powerful, has not been blessed with the same level of natural talent or gifted with latent superpowers. Everything Zoro has achieved has been through hard work and determination to be the strongest swordsman in the world. Even the three swords that Zoro currently wields -- Wado Ichimonji, Sandai Kitetsu and Enma -- require incredible strength to wield. While these three swords do increase the power of the user, their potential output is intrinsically tied to the abilities and strength of the wielder. Sanji's exoskeleton abilities, on the other hand, are not inhibited by limiting factors.
Sanji Doesn’t Train or Aspire to Be Strong
Unlike Zoro, Sanji has never made it his life goal to be physically strong. Strength, for Sanji, is a means to an end. It's a way for him to help his crew and achieve his dream of finding the All Blue. While Zoro is training his body and lifting weights, Sanji is cooking or hanging out with his friends. Somehow, though, there isn't a massive difference in power between Zoro and Sanji. Both have exceptional physical qualities, but only Zoro actively engages in training. However, considering Sanji's already considerable potential as a fighter, if he were to train and fully harness his body's capabilities during combat, his power could increase exponentially, unlocking new levels of strength and discovering additional techniques.
Through training, Sanji may be able to unlock additional powers that exist within his genetically modified body or better utilize his body's abilities. Recently, during Episode 1061, "The Strike of an Ifrit! Sanji vs. Queen," Sanji revealed a new ability called Ifrit Jambe, with which he can unleash even hotter flames than he could previously by combining his exoskeleton's enhanced muscle speed and strength with Armament Haki. This devastatingly powerful combination enables Sanji to quickly finish off Queen, sending him flying out of the castle with a forceful kick.
Sanji Is the Best-Written Straw Hat
In the entire One Piece series, Sanji may be the character with the best backstory and character development. At the beginning of the series, Sanji was little more than a loud, aggressive cook. He was portrayed as someone who could not back down from an argument and was constantly butting heads with Zoro. However, over time, Sanji becomes a more supportive and emotional person. During Episode 1057, "For Luffy? Sanji and Zoro's Oath," he asks Zoro to deal with him if he loses control. In this moment, Sanji demonstrates that he values the lives of his friends more than his own. This singular moment may best illustrate Sanji's substantial emotional growth he has experienced throughout the series. When Sanji made this request to Zoro, he needed the humility to ask this favor from someone with whom he has always shared a fractious relationship.
Emotions, passions and trauma have played a role in Sanji becoming a more powerful fighter. During the two-year time skip, Sanji's training under Emporio Ivankov on Momoiro Island left an indelible mark of trauma. This trauma enabled Sanji to develop two new potent techniques: Sky Walk and Hell Memories.
Since Sanji's introduction, there has always been an unspoken order among the Straw Hat's top three, with Monkey D. Luffy being first, Roronoa Zoro coming in second and Vinsmoke Sanji holding the third-highest position. Any time the Straw Hats engage in battle, Zoro and Sanji will fight the second and third-strongest opponents respectively. The charismatic chef Sanji's potential as a formidable force is often overshadowed by Zoro's.
However, beneath Sanji's laid-back demeanor lies untapped potential and hidden abilities that could one day overthrow the established ranking among the top three. As One Piece moves toward its conclusion, there are going to be a number of surprises, and one of them may well involve Sanji. Over the years, Sanji has transformed as a character, coming to terms with past trauma and growing tremendously as a person. Sanji stepping up and becoming Luffy's first commander would be a nice way to end his character journey.