well I mean, he's got a great ground string that can be hard to assist/punish properly. his dash seems to be fully invincible like minato's teleport because he turns into crows. as far as range is concerned fireball is only decent, but he's got some sort of chakra shuriken combo (may be a support drive). and "TURN DOWN THE SUCK, TURN UP THE SKILLS" is, as far as I'm concerned, not a valid counterpoint to susano'o. it only does four hits so even turbo substitute is not going to do much for you, and even ray didn't figure out any way to deal with it.
as far as mechanics go we pretty much have everything down - the game's not exactly guilty gear in terms of technical skill, and none of what exists helps against susano'o. he's immune to ninjutsu, ignores hitstun, his B melee chain counts as ranged so you can't substitute behind him, and running away doesn't work because he still retains his chakra dash. knj cancelling, arguably the highest level technique in the game, is useless thanks to aforementioned immunity.
I'd like to see this supposed superiority ranged characters have when susano'o is raping them in the face - I mean, I can see how, in general gameplay, ranged/turtle characters have an advantage, thanks to mashing on substitute marginalising the role of ground strings. but unless the best ranged characters are so much better than itachi that they can maintain a significant (>50%) health buffer prior to itachi going apeshit on them with susano'o, it really just seems like people talking air on forums, whereas we collectively spent several hours getting fucked in the face with a giant flaming sword.
sometimes cheap characters are just trashy noob-killers (mashing with raphael in socal comes to mind), but other times cheap characters are actually, well, rather cheap - especially in a game like this where I'm pretty sure balance was not an overwhelming priority for the designers.
tl;dr:
I'm still fairly convinced that itachi is top tier; I think the gameplan with the greatest chance of success is:
1. drop itachi's hp to just above awakening
2. sandbag until you have awakening
3. awaken
4. beat down itachi so hard he doesn't have a chance to awaken. watch out for BROTHERLY LOVE ruining your shit. if he does, you'll at least be on equal footing (kind of).
ostensibly this would also work well against other characters that have really strong awakenings. the question is, will matches between similarly high tier characters end with both of them turtling at low health, waiting for the other to knock them into awakening?