Confucius was never a leader. he was just a philosopher of the Zhou Dynasty. but then, his philosophies had shaped Chinese society profoundly; his concepts did not bring China backwards. China became an advanced civilization before it became backwards. if was the Chinese' failure to change and adapt that somewhat brought about its failure. not exactly a direct cause-and-effect.
i'm not sure about Qin. Qin Shi-Huang was somewhat like Mao, who unified the country but brought great suffering to people. at least he set the foundation for a prosperous China under Han Dynasty.
yah i would agree Han Wudi and Tang Taizong are better choices. Emperor Qianlong, too, deserves to be represented. but comes the problem: he's a Manchu.
what about Gandhi then? perhaps he is in the same position as Joan as well. i think another good choice for India would be Asoka.
i am puzzled why Montezuma was chosen for Aztecs. i thought i read somewhere he wasn't a very good ruler. again, maybe because he was more well-known.