Kakashi is no doubt a strong ninja, but you see they are in completely different leagues. Kakashi in part 2 has noted that he cannot defeat itachi alone after what happened in part 1, but also due to this decided to use gai's counter.
That gai's counter is rigged with failure, so much so that it fails at the very first hurdle, which is that itachi doesnt need his eyes for genjutsu.
The next thing people say is that kakashi can counter genjutsu with clones and although that is true, it holds very little substance in a 1 vs 1 fight. If you back to that fight (30% itachi clone vs kakashi). Kakashi created a kage bunshin to counter genjutsu, but you see he created that because he was depending on naruto to defeat the itachi clone. In a 1 vs 1 fight, due to his chakra, it wouldnt be wise for him to use a kage bunshin just to counter genjutsu.
Basically in a 1 vs 1 fight, i highly doubt kakashi would use a kage bunshin. Way too risky. Susano, yasakas magatama or even izanami is isnt a factor in this, it isnt needed. We even saw how kakashi struggled, to teleport susano's arrow because he couldnt evade it. He isnt evading amaterasu either and how is he teleporting amaterasu (if he gets the chance), if he is using gai's counter?.
I dont even want to stretch my legs in this thread because i dont need to.
Mid difficulty at best for itachi