I don't want to mock ZKK fans or Zoro fans in general more than doing jokes about it and friendly banter, but really, ZKK reads as something that would surely happen if Zoro was the main character of One Piece. And I don't mean this in a bad way, but maybe sometimes people overextend what importance certain characters really have when it comes to the main events of a story.
I'm almost sure that if One Piece turned out differently and ended much sooner or there was no Japanese-focused arc, Oda would have done the Nine Scabbards of a dethroned Shogun vs Corrupt Shogun and Dragon as a separate manga right after One Piece. But this is what we've got lol