Is Mandarin nonsense?

No, Mandarin is not Manchu. Manchu has its own language, grammar and writing, belonging to Altaic language family. Mandarin is a Sino-Tibetan language family, but now Mandarin is based on northern grammar and Beijing dialect. Mandarin is also changing, because the "participation" of ethnic minorities has changed the pronunciation and grammar of Mandarin. Southern dialect is not authentic ancient Chinese, because it is also changing, and it is not as big as Mandarin.