Did they know that reckless courage saved Sakura? He always has known his own level, but he fights either way for the sake of his friends. He didnโt mind being beaten, getting hurt or losing. He never expected to win. But he wanted to help
Without Nirei fighting Suo, Suo arc will never started. Without Nirei fighting Suo, Sakura would have given up even before finding Endo. Without Nirei, Suo would have simply disappeared and everyone would have simply think he had betrayed them all.