Because of astronomical gap in strength lol
Oni Giri is technique Zoro had it for years. He created it.
Then he used his post time skip amped up stats to add insane power to it
Then CoA to make it even stronger
Then CoC
Oni Giri is technique Zoro had it for years. He created it.
Then he used his post time skip amped up stats to add insane power to it
Then CoA to make it even stronger
Then CoC
Without technique to correctly apply them, those things mean nothing.
We know Zoro wants to become the strongest swordsmen in the world, and it's everything you mentioned and more that make that happen, not just one thing.
Zoro's original techniques, that are refined overtime
all 3 aspects of haki and their advanced versions
physical strength
It's all of those things