Kabuto thought it was impressive, and Madara (via Zetsu) called Itachi invincible due to his items. Your initial response also failed to grasp the question, as Hashirama, Madara, and Mū were not alive when Itachi was, and Kabuto, Sasuke, and Naruto certainly weren't defeating Itachi when Itachi was alive. The only half-correct answers are Nagato and Obito and there is nothing causal or even certain about their victories over Itachi as Obito steered completely clear of confronting Itachi head to head until he died naturally and Nagato was mentally and emotionally unbalanced in life.