Zoro and Sanji are two of the main fighters of the Strawhat Pirates, the protagonist group of One Piece.
Hailed as a powerful swordsman, Zoro is Luffy's right-hand man and the second strongest Strawhat after him. As such, the green-haired pirate acts as the crew's first mate. Meanwhile, Sanji is the cook of the crew and is usually considered to be the third strongest member of the bunch.
All One Piece fans know that Zoro fights opponents who are clearly stronger than Sanji's. However, not everyone agrees on how large the difference in strength is between the characters defeated by the former and those beaten by the latter. Follow this thread to find out a detailed analysis on the subject.
Disclaimer: This article contains major spoilers from the One Piece manga up to Chapter 1066 and reflects the writer's personal views.
In One Piece, Zoro defeats opponents who are typically a fair amount stronger than Sanji's
Mr. 1 is much stronger than Mr. 2
In the Arabasta arc, Zoro defeated Mr. 1, while Sanji overcame Mr. 2. Both were members of Baroque Works, a criminal organization created by Crocodile to destabilize and seize the Arabasta Kingdom.
In Baroque Works, male agents were ranked through numbered codenames that were given according to their strength. A lower number directly corresponded to a higher rank. Hence, Mr. 1 was inherently stronger than Mr. 2.
Mr. 1 ate the Dice-Dice Fruit, enabling himself to turn his body into sharp blades made of tough steel. This Devil Fruit power put him on a different level compared to Mr. 2. In fact, Mr. 1 was Crocodile's right-hand man and his strongest subordinate.
After both were arrested, Mr. 1 and Mr. 2 were imprisoned at Impel Down's Level Four and Level Three, respectively. Given that the stronger the prisoner, the higher the numbered level he is jailed at, this implies that Mr. 1 is a more powerful One Piece character.
Moreover, Mr. 2 was frightened at the prospect that Crocodile could send Mr. 1 to punish him if he failed the mission he was tasked with. This further establishes that Mr. 1 is a lot stronger than Mr. 2.
Ohm is remarkably stronger than Satori
In the Skypiea arc, Zoro defeated Ohm, while Sanji overcame Satori, both being Priests and the greatest followers of Enel. Each of the four Priests subjected the intruders of Sky Island to a challenge called the "ordeal."
Ohm's test, the Ordeal of Iron, was by far the most difficult of all four, having a 0% survival rate. However, Zoro became the first person to triumph against it and defeat Ohm.
On the other hand, Satori's test, the Ordeal of Balls, was relatively much easier, with a 10% survival rate. He was also weaker than Shura, whose Ordeal of String had a survival rate of 3%. Hence, it's a given that Satori was noticeably weaker than Ohm, who was the strongest of the four Priests and Enel's most powerful subordinate.
Zoro was able to defeat Ohm in a 1v1 fight. He had some trouble initially, but he didn't need to push himself to his maximum effort to defeat Ohm. Conversely, Sanji needed Luffy's help to beat the much weaker Satori.
Kaku is noticeably stronger than Jabra
In the Enies Lobby arc, Zoro defeated Kaku, while Sanji overcame Jabra. Both were members of CP9, a group of secret agents in the employment of the World Government. Kaku's Doriki was only a bit higher than Jabra's, but the difference in strength between them is much greater than those numbers would suggest.
In One Piece, Doriki only measures basic physical abilities. Thus, it didn't include Kaku's swordsmanship and his newfound Devil Fruit, which gifted him with new techniques and a new powerful final move.
While Kaku's basic skills are slightly superior to Jabra's (enough for the latter to admit his inferiority), his overall fighting abilities are much greater than his colleague's. In fact, no technique in Jabra's arsenal remotely compares to Kaku's Sky Slicer Rankyaku.
One Piece author Eiichiro Oda emphasized the high level of the duel between Kaku and Zoro with the Tower of Law shaking under the power unleashed by their clash. Instead, the battle between Jabra and Sanji received a different hype.
Kaku appears to be a noticeably more dangerous fighter than Jabra, with a greater number of strings to his bow and a far more powerful final attack. He has also received a better portrayal throughout the One Piece series, having been depicted as a sort of right-hand man for Lucci.
Among the entire CP9, only Lucci and Kaku were entrusted with a unique mission regarding Nico Robin. This implied that their strength was greater than others, who, including Jabra, weren't given any special assignment.
After the time skip, Kaku and Lucci returned much stronger than before. They were promoted to CP0, the greatest Cipher Pol. Unsurprisingly, Kaku was the only former CP9 member on Lucci's side.
Zombie Ryuma is blatantly stronger than Absalom
In the Thriller Bark arc, Zoro defeated the zombie version of Ryuma, while Sanji overcame Absalom. Both were part of Warlord Gecko Moriah's army.
The zombie created by the legendary swordsman of Wano paled in comparison to the original, who was one of the strongest One Piece characters of all time. However, it was still powerful. Even holding back and using merely a fraction of its strength, the zombie easily defeated Brook.
Brook was saved by Zoro, who took his place in the battle. After a thrilling duel, which Brook and Franky watched astonished, Zoro defeated Ryuma's zombie. The latter was a dangerous enemy, with the speed and power of his attacks being on a whole different level than Absalom's.
The leader of the Zombie Soldiers and Zombie Generals, Absalom ate the Clear-Clear Fruit, which allowed him to become invisible, using his weapons and physical strength to attack the unaware opponent.
However, he didn't stand a chance against Sanji. While the latter wasn't able to finish him, he completely outclassed him, weakening him to the point that even Nami's technique was enough to put him down for good.
Absalom doesn't seem as threatening as Zombie Ryuma, who could beat a Mid Trio level fighter effortlessly. Brook and Robin of Franky, who didn't stand a chance against the zombie, would likely be more than a match for Absalom.
Killer is easily stronger than Page One
In the initial part of the Wano arc, Zoro defeated Killer, while Sanji overcame Page One. Being one of the Eleven Supernovas and the right-hand man of Eustass Kid, Killer was a far stronger fighter than Tobi Roppo member Page One.
Admittedly, Killer was nerfed during that fight. Working as an assassin under the alias "Kamazo," he was equipped with two scythes instead of his two blades called "Punishers." While he showed great skill in using these scythes, they still pale compared to his weapons of choice.
It must be said that Zoro was nerfed as well. Out of his three swords, he only had two, lacking the Shusui, which at that time was his most powerful blade. His body was also weakened as a result of eating poisoned food.
Moreover, Zoro was facing Killer and another opponent in addition to him simultaneously. Fighting in 1v2, he lost focus on Killer and suffered a serious injury when the latter struck him from behind.
However, Zoro's strength was greater than Killer's and he managed to overpower him anyway. With his superior physical strength, he disarmed the latter of one of his blades and used it as a sort of third sword to perform a Three Sword Style attack. The move left Killer annihilated.
Conversely, Page One was depicted as the weaker member of the Tobi Roppo of the Beasts Pirates. With Tobi Roppo generally paling in comparison to the Red Scabbards, who Killer easily outclasses, Page One didn't seem like a threatening fighter compared to Kid's right-hand man.
Page One managed to put some pressure on Sanji despite the latter using his Raid Suit, which greatly improves his durability, speed, and physical strength. However, Sanji was likely testing his abilities. If he had gone all-out on Page One, he would have probably defeated him.
King is a lot stronger than Queen
In the final part of the Wano arc, Zoro defeated King, while Sanji overcame Queen, both being part of the All Stars of the Beasts Pirates. However, within the All Stars, King had a special status that set him apart from his two colleagues.
King was Kaido's right-hand man and his strongest and most loyal subordinate. The latter personally recruited him as his second-in-command after witnessing his strength and being impressed by it.
Kaido assigned him the name "King" to replace his real name, Alber, to emphasize his remarkable fighting capabilities. On the contrary, the Emperor never praised Queen's strength throughout One Piece.
With the hierarchy of All Stars being based on poker, where the "king" card holds more value than the "queen" and the "jack" cards, the formerly-called Alber is implied to have a far superior status compared to Queen's.
Much faster, physically stronger and with more dangerous attacks, King is shown as a better fighter than Queen overall. Instead, the latter appears to be a mad scientist than a warrior. Queen is often clumsy, losing focus and even hitting himself.
No technique in Queen's arsenal remotely compares to King's Lunarian and Zoan powers. King is so tough that he can come unscathed from Zoro's attacks, despite these hits being powerful enough to injure Kaido. Instead, Queen was hurt by inferior strikes.
King can fly at high speeds to dodge incoming attacks and charge his opponents. Using his Lunarian powers, he can trade some of his exceptional durability for a further boost in speed.
Conversely, Queen is slow and static. He cannot dodge, primarily relying on his passive durability as an Ancient Zoan to survive the incoming attacks. Thus, if the enemy targets Queen with a move powerful enough to injure him, he is pretty much screwed.
Final Thoughts
Throughout the One Piece series, the opponents Zoro has defeated are stronger than the ones Sanji managed to beat. Depending on the issue, the gap between their arc opponents can fluctuate, but Zoro's arch-enemies are never weaker than Sanji's.
Sometimes, Zoro didn't defeat his opponents but still performance well against them. This happened against Fujitora in Dressrosa arc and against Kaido and Big Mom in Wano arc.
In comparison, during Dressrosa, Sanji was immediately overwhelmed by Doflamingo in one of the most one-sided fights in the entire One Piece series. In Wano, he didn't even meet Kaido and Big Mom, let alone fight them valiantly.
Even against opponents of similar strength, such as Vergo and Pica, Sanji's performances are noticeably inferior to Zoro's. While Sanji was overpowered by Vergo, despite the latter holding himself back, Zoro completely annihilated an all-out Pica.
Moreover, when Zoro overpowered his enemies, he did that with greater dominance than Sanji was able to do with his. Hence, it can be said that he achieved better accomplishments than Sanji. This is not surprising, given that no Strawhat member receives the same portrayal as Zoro in One Piece.
The author sometimes puts Sanji in a similar class to him, as the two wings that are Luffy's biggest pillar within the crew, but he also sets Zoro apart, placing him on a higher pedestal in strength and prominence. The green-haired pirate is emphasized as Luffy's right-hand man, sharing many strength-related accomplishments with him.
A testament to that has been seen in countless statements and scenes in the manga, as well as concurring information from the databooks and other One Piece media. All of these depict Zoro as the indisputable number two of the Strawhats, with his strength being second only to Luffy's.
While not being officially proclaimed the vice-captain of Strawhats, Zoro acts as one. He derives his authority from his superior strength. With his attitude as a Conqueror, his dominant leadership, and his wisdom, Zoro has been shown to fulfill this role in the best possible way throughout the One Piece series.