Sword-Style = Cooking Recipes
Stats/Powers (What Fuels your Sword) = Ingredients
This means that Oden is saying that his Techniques are Greatest, but it doesn't automatically translate to him being Best Swordsman,
We as Readers know that Greatest Sword-Style is Zoro's, it always has been since Chapter 1, but He is on a Journey to Upgrade his Stats/Fuel, that's the only way to become Best Swordsman,
Just like Sanji's Cooking is No. 1 Contender since East Blue, but He is looking for Ultimate Ingredients in All Blue,
Just like Usopp's Sniping is No. 1 Contender since East Blue, but He keeps finding new ways to Upgrade his Arsenal/Ammunition,
Just like Nami's Weather Sense is No. 1 Contender since East Blue, but She keeps learning more & more about what kind of Weathers there are,
... etc
Zombie Ryuma & Brook are Best Proof of how Sword-Styles work,
Zoro's Fight against Ryuma showed us that Brook's Sword-Style is Extremely Close to Zoro's, but the reason Brook is No Match for Zoro is cuz of their Stats (What Fuels their Sword), as Simple as that,
Oda said that He gave Zoro Three Swords so that it's one more Sword than Miyamoto Musashi, so aside from Zoro, Oda does consider Two-Sword Style to be an Extremely High Level Style, those who truly Mastered it are worthy of Great Respect, these Include:
Oden + His Retainers who were able to Copy his Style
Vista
Ushimaru
Shiki
(Crocodile is also Theorized to be a Former Two-Sword Style User)