I started to think about this during the current fight. It seems to me that Luffy is becoming much stronger than Sanji and Zoro, he is basically in another league.
Before the Time Skip
- I feel that at the beginning of the manga they were somewhat on the same level. Well, obviously Luffy was stronger, but not too much. His fight against Sanji/Zoro would have been very difficult.
- The situation changed when they faced CP9. While Zoro and Sanji got two new moves (Ashura and Diablo Jambe), Luffy stepped up to the next level (as Luffy said to Blueno: “All of my techniques will evolve one step”). I think that the big difference in Doriki between Lucci (4000) and Kaku&Jabru (2200/2180) is not accidental. I am confident that neither Zoro nor Sanji could have handled Lucci. So, Luffy in his Gear 2 and Gear 3 became much stronger than Sanji & Zoro. Luffy against Sanji/Zoro is now an easy win for Luffy.
After the Time Skip
- We know that one can improve their Haki in battles.
- Both Zoro and Sanji had almost zero chance to improve anything. Basically, they didn’t have many fights with Haki users. Sanji only had several very short clashes with his opponents, and Zoro used Haki a couple of times with Pica.
- Luffy, on the other hand, fights as crazy and almost always uses his Haki. Coliseum, Bellamy, Doflamingo & Trebol, Cracker, Big Mom’s army, Katakuri – a lot of fights against Devil Fruit and/or Haki users. And it seems that during the fight with Katakuri he will upgrade not only his Observarion Haki, but his Armament Haki as well (at least now he blocks Katakuri’s armament punches without flinching from pain).
Where do they stand against each other and against the strongest fighter of the New World at the end of Whole Cake Island?
- I think both Sanji and Zoro caught up to Luffy (without Gear 4). I see it like this: Luffy was training in all his gears, while Sanji and Zoro were training in their base forms (well, they don’t have other forms).
- I think that the G2&G3 -> G4 powerup is bigger than G1 -> G2&G3 powerup. Therefore Luffy (G4) is much stronger than Zoro/Sanji (I would say they have no chance against him).
- I think Doffy is stronger than Sanji, Zoro or Luffy (w/o G4): Sanji, Zoro, Luffy (w/o G4) < Doflamingo < Luffy (G4) I see neither Zoro nor Sanji winning against Doffy (especially with his awakening).
- Sweet Commanders are obviously stronger than Doffy. Luffy was able to hold his own against Doffy with G2/G3, but Cracker almost immediately overpowered Luffy and forced him to use G4.
- We also have so-called “monsters” amongst Big Mom’s crew (according to Vito) – Over, Perospero, Compote, Daifuku. Where do they stand in terms of power? Judging by Perospero’s bounty and strength ( 700 000 000 beli, easily dispatched Chopper, Brook, and Pedro) they are somewhere on the same level as Doffy (maybe a little bit weaker?).
- So, now: Sanji, Zoro, Luffy(w/o G4) <= Oven, Perospero, Daifuku <= Doffy < Sweet Commanders < L(G4) < Big Mom
Basically, I think that Luffy can fight with almost any opponent (Admirals / top-tier Yonko Commanders) while Zoro and Sanji can win only against middle-tier Yonko Commanders / Vice Admirals. I think that neither Zoro nor Sanji had enough fights with strong opponents after the TimeSkip.
TL;DR At the beginning of the manga Luffy, Zoro and Sanji were pretty close in terms of strength. Now Luffy is simply in another league.
*Theory by fandrfa