Yata mirror doesn't grant wide range of defense
Totsuka blade is alsolimited by the speed of Itachi [which is considerably low comparing to current Sasuke etc..]
Tsukuyomi will make him weak as well and it wont be useful against powerful opponents with huge chakra capacity [who can break out of it as well]
Lets take the obviously biased argument for granted: Yata doesnt provide wide range of defense.
-Was big enough to stop 8 gigantic dragons/snakes from killing him
-Even so, it's fortes, as in, can chance its properties and reflect any/all attacks still stands and makes it OP
Speed
-Itachi was on par with Bee+Naruto and got a 5 in databook.
If someone bypass the susanoo/yata he has enough time to react to any attack.
Technically only Sasuke can break out of it.
If you wanna maximize it the possibilities, only MS users can break out of it. So Madara/Izuna/Shisui/Obito/Sasuke.
There are plenty powerful shinobis with huge chakras without MS so they are doomed.
And since when its tsukuyomi useless and not useful(even against powerful opponents?)
Thats such an ignorant argument I cant even...