Were are you getting YOUR information itachi used the sword to seal Pain in one hit! And he did that since being revived of course and after regaining control via that bird inside of naruto... AND for your next point itachi is stronger then he was back when he was alive... because now he has unlimited health and chakra, plus when he was alive he had a weakness from his illness. So....
Yes I was never being totally serious about itachi being the strongest! And the series Naruto still has some balance and understanding it's not like DBZ... but I must admit I loved it when planning something out and using team work could over come a stronger enemy who has rare and powerful abilities.
But even if I am not totally serious about itachi being as strong as I am saying... I truely believe he still has the sword and shield... or at least the sword! Which means if he can land one hit on Sasuke,Tobi, or Madara he would seal them and beat them. And the mirror probably has better defenses then even susano! So yes itachi just recently used that sword on pain...
So that means itachi has beat both orochimaru and pain in 1 hit each! Thats well beyond the strength and power of anyone else I can think of in the naruto world. I don't think Naruto or Sasuke could do that yet. Not to mention itachi has never used the yata mirror in combat only to tease sasuke near the end of there fight. Who knows how good the mirror really is it also looks like it only blocks things from one side.. meaning you can probably use it and the sword at the same time easily and the only weakness I can assume the sword and shield have is heavy chakra drain or strain on the body. Both of which should be nullified by the impure resurrection.