Since Sanji is one of the Straw Hat Crew’s top fighters, there has been a huge misconception of where his character stands when it comes fighting and how strong he is exactly. Now power scaling in One Piece is all over the place but let me explain to you why fans can’t understand Sanji and his fighting capabilities.
When we first saw Sanji in the Baratie, his first opponent was Gin and although he didn’t win that fight, it’s kind of shown what kind of fighter Sanji is.
Yes he uses his legs to fight but he also uses anything to his advantage, for instance, when Gin had him pinned down to the ground, Sanji spit the cigarette bud at Gin’s face in order to escape. Another instance of this is when he fought against Kuroobi in Arlong Park, he breathed air into the fishman’s lungs in order to escape and then beat him.
Sanji is the smartest outta the Monster Trio, he always uses his intelligence in a fight. That’s why all of Sanji’s opponents have always been tricksters like Bon Clay for example and his devil fruit ability the Mane Mane no Mi which allows you to turn into someone else; Bon Clay used his ability to trick Sanji by turning in to Nami and then was able to get hits on him, but Sanji later saw a flaw in his technique and further beat him.
Another example of this was in Water 7 when Sanji was on the Sea Train and noticed how Wanze used skates that can light up on fire due to friction, and after that when Sanji clashed with Blueno he couldn’t do damage because of the iron body technique.
Then jump to Enies Lobby when the Monster Trio got power-ups. I couldn’t help but notice that Sanji’s power up stood out from the rest: Diable Jambe was made for to counteract the iron body technique and burn through the defenses. Ironically enough Sanji fought the wolf zoan user Jabra who was a liar and who was said to be able to uses iron body while moving.