Looks the PRC censors don't teach history in China. Can't really blame people like you for that.
The UNSC seat was for the Nationalist party which is in present day Taiwan. It was because of the Sino-Soviet split that the US gave the Taiwanese seat to PRC in 1971. So present day China had not say in the UNSC until the 1970s
And WWII it was the British Indian troops that finally rescued East Asia from the Japanese along with the Americans. Infact, British Indian troops also helped in defeating the Boxer rebellion and occupying Shangai.
Do read
The Hindu : News / National : The forgotten history of Indian troops in China
And China does not represent the SCO, nor does it represent anything other than its own interests. A quick look at Chinese vetos shows what is important to them.
On the other hand, India despite not being a P5 member was always a strong voice for independence movements in Asia and Africa, while China under the PRC took a low key easy route.
