Danzo beats itachi with or without KA.
Against sasuke he didnt have shuishi's eye,which would have allowed him easily see through any genjutsu,he used his normal eye.
Danzo even beat sasuke in a cqc clash without the use of his sharingan,and put a seal on him,with the sharingan wich allows him predict itachi's moves,alongside his izanagi and fuuton. He wins
Don't assume things that give danzo an edge. Itachi is the best genjutsu user in the series, he's placed tons of genjutsu on people with sharingan before and danzo can't do shit against tsukiyomi.
Katon > Futon
Izanami > Izanagi , plus Itachi would instantly recognize when danzo uses izanagi and begin preparing a counter
Itachi is much smarter than sasuke and probably danzo too.
Danzo took like 12 lethal shots from sasuke's susanoo and other attacks, one shot from itachi's susanoo would seal him.
Itachi's first plan would probably be to cut off danzo's sharingarm since he would know that's how the izanagi works.
The list goes on. There's a reason why Danzo feared itachi and didn't just have sasuke killed anyways at the first plausibly deniable chance.