U missed a pt. Which was most imp......it is that izanami requires time to get ready(as Itachi said).....
U must record the outcome in ur mind and implement it into the opponents minds constantly looping it....the opponent can only escape if he realises and calms his mind and acknowledges himself and the situation...
To be frank,if it wasnt for sasuke,I dont think itachi wud hv won,I will give u 2 instances-one,in the beginning and kabuto vibrated the surroundings he could hv gone for Itachi(itachi might hv saved himself but Kabuto also wud hv struck faster without thinking much)...second,Itachi wud not hv been able to escape Tayuyus genjutsu as Sasuke used his tsukuyomi to help Itachi come out of it.....
But Izanami is not an OP move,it requires time for preparation,sharp mind to seek circumstances,and ur opponent has to be blind with power or hv an identity crisis,unwilling to face the reality..