lol, all of you have been mislead.
No wonder you all blaming oda about koh thinking its just the same power up but ut make sense anyone will jump to conclusion seeing zoro use koh right after flash-back about mihawk.
Next chapter is where we will see the gain.
Koh offcourse will remain unchanged, all zoro did is use acoc and acoa together in the final panel.
Zoro put on his bandana and activated koh he has yet to achieve the full Mastery he want but he already has a hint with lightning coc slash and he just need to reproduction that feeling for now and make it stronger for the real breakthrough in the final part of their fight.