The main problem here is that China actually has legitimate territorial claims in all of these disputes. In fact, from what I have read, China's claims to the South China Sea islands are stronger than any other claims. The Philippines, in particular, seems to be opportunistic and only jumped in with a claim after oil was discovered. China had been laying claim well before oil even became a major resource. Vietnam is the only country with a well-supported claim as I understand it. Obviously, China's claim to Taiwan has widespread international recognition. East China Sea is more shaky, but the claims from China are not baseless. It is not really the same situation that you had with Crimea, where Russia clearly and unequivocally recognized Ukraine's sovereignty over Crimea along with the rest of the international community.