Susano'o is not that strong, Itachi had Kata's Mirror which deflects all attacks, and Totsuka's Sword which is capable of sealing the soul of anything that it touches, plus it puts an enormous strain oon the body
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I would say the strongest is the reaper Death Seal which ws only usable by two people both of which were at kage level, the move itself was able to seal the nine-tailed fox, two hokages, and the arms of orochimaru.