Why is Sakamoto considered to be a legendary assassin?

In the early story, Sakamoto is insanely strong, making it clear why he is considered legendary. However, as the story progresses, stronger characters start to appear, and he gets powercrept little by little. Now, he can’t even beat Torres, who isn’t even trying to kill him. Sure, he’s not the same as he was five years ago, but the power difference shouldn’t be this drastic. If such powerful characters have existed all along, why is Sakamoto still regarded as a legendary assassin?