Your premise is very misguided and biased. You didn't account for the fact that Itachi was caught off guard by a Karasu bunshin - even Sage Mode sensors can be put off guard, as shown by how Kabuto was put off guard by Magatama, thus allowing himself to be nailed by Sasuke's Susano'o arrow
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- a Susano'o arrow being the very reference point you were drawing a comparison to. Further proof that Itachi only landed a hit due to Kabuto being caught off guard is that Kabuto reacted in time and stabbed Itachi the first time he tried to blitz
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(a part which you decided to ignore) and received the blow due to being tricked by a clone, rather than outsped to the point where he couldn't react.
Also, Itachi was going for a more serious strike than just Kabuto's horn, yet Kabuto was still able to react in time to
mainly evade Itachi's strike to the point where he only lost a horn.