And then it reinforce my speculation versus your speculation, i say Ashura comes from Sandai, you say it comes from Zoro..
again, we have a panel of Sandai Kitetsu’s creator talking to Zoro and he never once says anything about this… In fact the creator is talking about Enma and Enma’s ability and how Zoro has to overcome Enma… He never once says “Oh yeah and this is how Ashura that comes from my sword that I created works”
And no, nothing you say about Shusui giving zoro CoA will ever not be headcanon… this genuinely bizarre because at least with Ashura Oda is yet to actually give a concrete explanation so you can make up your headcanon about its origin… Shusui is out of the story… We are never going to return to this sword ever again… So there is literally no way the actual manga will ever confirm your random headcanon that Shusui creates CoA… so basically you are making up a statement that can never be proven or disproven