I don’t think that’s true at all? From my experience and research, China seems quite proud of it’s diversity. The five colors of the original ROC flag symbolized this diversity, though a bit simplified, as the “Five races under one union” (han, manchu, mongols, muslims, tibetans). This term is one of the “Three Principles of the People” formulated by Sun Yat-sen (who founded KMT and is venerated in both mainland China and Taiwan). It’s foundational to both Chinese republics.

(but if we’re talking about the language, then “Chinese” is mandarin Chinese unless otherwise specified)