Y'all whining about "muh nippon stronk" are little bitches. Adam's fight wouldn't have been half as emotionally affecting if he won, and Sasaki's fight would have been a huge anticlimax if he lost. Ignoring the future fights, because people commenting on this hadn't seen them, the setup is obvious-
Lu Bu, the most powerful human, tries to compete with the gods in sheer strength and is utterly overwhelmed.
Adam fights the gods with their own power and is once again defeated by the overwhelming unfairness of the gods. In dying, he inspires humanity to fight against the gods.
Sasaki Kojiro, a loser who knew he couldn't defeat the gods on their own battlefield, challenged Poseidon on his own terms, and in the process won the first duel of his life.
This shit is storytelling 101. Yeah, Sasaki is a Japanese dude. He was also the perfect character archetype to get humanity's first win- someone who wasn't going to attempt to take on the gods on their terms.
Also, "muh nakama" fuck off, y'all're just jaded. Sasaki as a character represents a man who gained everything he had from the stronger, more experienced swordsmen before him. Obviously it's gonna be "muh nakama," that's his gimmick.