edo Itachi > Itachi prime
Since the return of Itachi ,i feel that his latest techniques to power up are made to avoid Itachi being surpassed by the others and keep his status.
First the Magatama and now Izanami.
Although I must admit that Kishi is very clever to get the pill.
It is known that Itachi does not have the strength of Sasuke's or the chakra of Madara, his strength is intelligence.
Normally using Tsukuyomi and amaterasu almost take all his chakra,Kisame is forced to carry him such itachi was exhausted.Not to mension that susanoo kills him..
When you know that the Magatama is his most powerful attack which is launched by Susano'o, we understand why in his lifetime he didn't use it,since he would die.
And Izanami, one understands even further, he would lose those two eyes squarely.
The truth is that the edo itachi we see is by far stronger than Itachi in his prime lifetime who was neither an endurance monster or a monster of chakra.
Nagato would wreck Itachi.