We got
DB hyperbole and a character who earlier in the fight implied Hebi Sasuke's expertise with 3T made him better than MS Itachi... character opinions and DB hyperbole are not reliable, and only exist to hype the character/technique. Kishimoto employs character perspective, which makes it more realistic. It means characters make opinionated statements and make assessments based on only what they've witnessed, rather than just fact. Hence why BZ became invested in the idea that Kirin was unavoidable, when we know that teleporters could evade it. And hence why throughout his statements on Itachi's Susano'o and its tools, he kept saying things like "or so it seems", "so the legend goes" and "It looks like".
The guy didn't even realize Itachi was ill until he was coughing up blood and having a heart attack.
What is clear, is that it does not make him invincible. Invincibility suggests that Itachi cannot be overcomed whilst his complete Susano'o is active, which is a fallacy because:
a) Yata is attached to his Susano'o. If Susano'o is blasted away, then Yata is deactivated.
b)
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Aside from being obliterated along with S'O when Kirin hit, it's best feats are tanking 7 or so Fudas and repelling Sasuke's sword.