And how do you know that Itachi wasn't letting himself be hit to get closer to Kabuto and that Mikoto need not resort to such tactics. How do you that Itachi getting hit wasn't for suspense or plot or to make it look interesting or to make Kabuto look less useless before he gets demolished by Izanami. What I'm saying is, any Uchiha, any Uchiha at all, could look at him and use Izanami and he's done for in that one jutsu shot. Thank the manga.
Itachi didn't let himself be hit constantly; the only times he allowed himself to be hit were when his Karasu Bunshins got hit to start and end Izanami.
The rest of the times Itachi was hit because he just couldn't do anything else, hence Sasuke's intervention and why Edo Tensei's regeneration came in handy.
Plot or not, the evidence shows Itachi got hit and only shows two times where he actually allowed himself to be hit. Other times it was all Kabuto's 'wins'.
If Izanami is a one-shot jutsu, then Itachi wouldn't have needed to be hit twice
in precisely the same manner. If Itachi with the Mangekyou Sharingan, fighting
alone, couldn't manage to land Izanami without the help of Sasuke - who isn't exactly "any Uchiha" - then I'm not inclined to believe that Mikoto can do any better. Specially when she lacks the Mangekyou.
