The single most important factor to becoming a stronger swordsman is Haki and Haki alone. Nothing else (skill, physical strength, endurance, etc..) even registers. Indeed, it wouldn’t be wrong to say that true “sword skill” is just the strength and proficiency of your Haki.
Arguments in Favour
Some credible arguments in favour:
- Koshiro told Zoro that the pinnacle of swordsmanship was the power to protect what you wanted to protect and cut what you want to cut.
- The ability to cut only that which you want to cut is “Ryuo”.
- Thus, the pinnacle of swordsmanship cannot be reached without Ryuo.
- Zoro’s bloom in his fight against Daz Bones was a bloom of Haki.
- He subconsciously manifested Busoshoku Haki (the breath of all things) and Kenbushoku Haki (knowing where the rocks wouldn’t fall).
- Zoro’s trump card against Pica was Busoshoku coating.
- Indeed, he said that Pica would beat him if only his Haki was stronger.
- Luffy’s Haki teachers were all swordsmen.
- Rayleigh during the timeskip.
- Hyougoro during Wano.
- As far as we’re aware, the only thing Mihawk taught Zoro was Haki.
- He specifically forbade Zoro from drinking wine until he mastered coating his swords with Busoshoku Haki.
- Zoro has not other flashbacks showing him learn anything else.
- Recall that Zoro asked Mihawk to teach him “the way of the sword”.
- Thus, “the way of the sword” is nothing other than mastery of Haki.
- Black Blades — the pinnacle of swordmanship — are forged through supreme Haki.
- Mihawk told this to Zoro.
- Gyukimaru reiterated it.
- Only the greatest swordsmen of all time have wielded Black Blades:
- Former WSS: Ryuma
- Current WSS: Mihawk
- Future WSS: Zoro
- Lesser swordsmen have failed to forge Kokuto
- Zoro’s growth with Enma was all about mastering his Busoshoku and Haoshoku Haki.
- Enma forcibly released his Ryuo, and learning how to wield Enma forced him to temper and master said Haki.
- He had to unlock Haoshoku haki to effectively use Enma at all.
- King stated that Zoro had “kingly ambitions”.
- Upon witnessing his “King of Hell” mode, he chastised him not to get ahead of himself as Kaido would become the Pirate King
- That is, King considered Zoro a worthy contender for the Pirate King throne.
- Zoro’s big power up post timeskip was unlocking Haoshoku coating and developing an associated mode: “King of Hell”.
- His big attack against King was entirely dependent on his Haki with “skill” and physical strength being completely irrelevant.
- This is his equivalent of Luffy’s Gears.
- Asura may also be a manifestation of Zoro’s Haki.
- It was only after his Haki bloom in Wano that Zoro earned the title of “Kengou” (master swordsman).
- Mastering his Ryuo
- Unlocking Haoshoku
- He needed this to tame Enma
- Unlocking Haoshoku coating
- Unlocking a new mode (“King of Hell”) based entirely around Haoshoku coating
- Unlocking a super move that use massive amounts of Haoshoku coating
- At the end of his fight with King, Zoro stated that he will become “Jigoku no Ou” (“The King of Hell” [and a pun on “The King of Samurai”]).
- This further reiterates how important Haki — and Haoshoku Haki in particular — is to the pinnacle of swordsmanship.
At the high and top tier, swordsmanship is — as best as we can tell — solely about Haki. That is, the statement that Mihawk’s swordsmanship surpasses Shanks is a statement that Mihawk’s Haki surpasses Shanks’ Haki.
For if Shanks had the superior Haki, he would be the superior swordsman.
*Theory by Cinera