Shanks is like Roger: incredibly powerful Haki, but more Haki focused/all around focused, than Sword focused. IMO, Rocks was similar: their Swords are conduits for their techniques.
The difference?
Swordsmen have blades that have ACTUAL personalities: we know this because of @nik87 , and Oda drawing Zoro's blades with faces with personalities:
This is the difference.
Since Roger is Roger, I think it's possible he passed the gap, and Ace had a personality: but, overall, Roger wasn't a true Swordsmen. Why? No Black Blade. Oden came close, IMO, and so did Rayleigh, Roger, and Newgate:
The difference? Zoro treats his blades like living people. Sanji treats knives like cooking tools.
Zoro risked death to chase his blades falling off of Onigashima vs King, a man who had been bodying him. Zoro's Blades are like Luffy's Straw Hat: they are his Nakama, his Treasure.
Kamusari has been used by two non-Swordsmen: Roger and Shanks.
Mihawk has no interest in fighting Shanks, because Mihawk wants Swordplay: he trained Zoro, because he wants to fight strong Swordsmen. Why did Mihawk show Vista so much respect in Marineford? Mihawk is the Marine Hunter, and hates Marines. He respects true Swordplay/Honor: he complimented a random Swordsman he met for the first time, Zoro, and asked him to seek him out. Shanks was more swordplay focused before Luffy had him lose his arm: this was his duel with Mihawk. But, losing his arm made Shanks Haki focused, so Mihawk didn't want to fight him anymore, because Shanks was no longer Sword-Focused.
Kamusari is Divine Avoidance: I believe Germa was originally part of the World Government, but seceded. This fits Sanji running from the Straw Hats.
Zoro and Sanji will surpass Shanks and Mihawk, by combining Sword Skill + Haki + Basic Combat (I think EOS Sanji will use Flaming Cooking Knives):
Oda foreshadowed this line with one of the most badass panels in the series, where Zoro talks about ripping out King's throat:
EOS Sanji will use Flaming Knives, as teased by Sanji defeating Wanze with Knives of the Sea Train
EOS Zoro will be a Swordsman who's willing to fight dirty, like King
King taught Zoro the truth Kaido knew: Haki Transcends All
But, Sanji won't use Kamusari with his Knives
Kamusari = Divine Avoidance
To Sanji, two things should never be hurt/abused: Women, and Food. Sanji's refused to hurt Women and Food the entire series. To him, Women and Food are literally Divine Avoidance
His hands will avoid any damage.
His Kamusari Haki Skill, will cut through all.
EOS Sanji won't even have to worry about his hands being damaged.
His Haki will cut through everything, without burning the food with his flames, nor scarring the lady's with his sharp style.
Kamusari Sanji cuts them clean down the middle.
Only Shanks learned Kamusari on the Roger Pirates, as far as we know
Sanji and Zoro will surpass Roger's Crew, by both learning Kamusari themselves
I think Momo will forge Sea Stone Armaments for all the Straw Hats
I think Hiyori, in honor of the man who was Boiled, Oden, will help forge Sanji's Cooking Knives, that will burn White Hot with his Haki of Love.
Sanji's White-Hot Knives and Legs soaked in the Flames of Love will cut through these Celestial Dragon bastards with Kamusari
Sanji has spent his entire life rejecting royalty for the sake of kindness.
Sanji rejected Germa, who sucked up to the WG they hate, for his true feelings.
Sanji IS Divine Avoidance: a Simp, who would never treat women the way the World Government does. A man who always rejected royalty/nobility/worship, because he wanted to be kind.
The difference?
Swordsmen have blades that have ACTUAL personalities: we know this because of @nik87 , and Oda drawing Zoro's blades with faces with personalities:
This is the difference.
Since Roger is Roger, I think it's possible he passed the gap, and Ace had a personality: but, overall, Roger wasn't a true Swordsmen. Why? No Black Blade. Oden came close, IMO, and so did Rayleigh, Roger, and Newgate:
The difference? Zoro treats his blades like living people. Sanji treats knives like cooking tools.
Zoro risked death to chase his blades falling off of Onigashima vs King, a man who had been bodying him. Zoro's Blades are like Luffy's Straw Hat: they are his Nakama, his Treasure.
Kamusari has been used by two non-Swordsmen: Roger and Shanks.
Mihawk has no interest in fighting Shanks, because Mihawk wants Swordplay: he trained Zoro, because he wants to fight strong Swordsmen. Why did Mihawk show Vista so much respect in Marineford? Mihawk is the Marine Hunter, and hates Marines. He respects true Swordplay/Honor: he complimented a random Swordsman he met for the first time, Zoro, and asked him to seek him out. Shanks was more swordplay focused before Luffy had him lose his arm: this was his duel with Mihawk. But, losing his arm made Shanks Haki focused, so Mihawk didn't want to fight him anymore, because Shanks was no longer Sword-Focused.
Kamusari is Divine Avoidance: I believe Germa was originally part of the World Government, but seceded. This fits Sanji running from the Straw Hats.
Zoro and Sanji will surpass Shanks and Mihawk, by combining Sword Skill + Haki + Basic Combat (I think EOS Sanji will use Flaming Cooking Knives):
Oda foreshadowed this line with one of the most badass panels in the series, where Zoro talks about ripping out King's throat:

EOS Sanji will use Flaming Knives, as teased by Sanji defeating Wanze with Knives of the Sea Train
EOS Zoro will be a Swordsman who's willing to fight dirty, like King
King taught Zoro the truth Kaido knew: Haki Transcends All
But, Sanji won't use Kamusari with his Knives
Kamusari = Divine Avoidance
To Sanji, two things should never be hurt/abused: Women, and Food. Sanji's refused to hurt Women and Food the entire series. To him, Women and Food are literally Divine Avoidance
His hands will avoid any damage.
His Kamusari Haki Skill, will cut through all.
EOS Sanji won't even have to worry about his hands being damaged.
His Haki will cut through everything, without burning the food with his flames, nor scarring the lady's with his sharp style.
Kamusari Sanji cuts them clean down the middle.

Only Shanks learned Kamusari on the Roger Pirates, as far as we know
Sanji and Zoro will surpass Roger's Crew, by both learning Kamusari themselves
I think Momo will forge Sea Stone Armaments for all the Straw Hats
I think Hiyori, in honor of the man who was Boiled, Oden, will help forge Sanji's Cooking Knives, that will burn White Hot with his Haki of Love.
Sanji's White-Hot Knives and Legs soaked in the Flames of Love will cut through these Celestial Dragon bastards with Kamusari
Sanji has spent his entire life rejecting royalty for the sake of kindness.
Sanji rejected Germa, who sucked up to the WG they hate, for his true feelings.
Sanji IS Divine Avoidance: a Simp, who would never treat women the way the World Government does. A man who always rejected royalty/nobility/worship, because he wanted to be kind.