Taiwan Japan and south Korea themselves can't pose threat to china, but they can with the US support. The same apply to India.
The most things to concerned about is India security contradict with Chinese security which not gonna go well for cooperation like SCO that have security as a primary goal. This is why India being trojan for US favor. A huge Russian mistake.
You are conflating 2 things:
1) whether or not India is a threat China really needs to concerned about in a westpac scenario. Like, can it offer Japan or Australia level of help to America
2) Whether it should be in SCO
You are using 2) to argue for 1), which is just not a serious argument.
Explain to me in military terms, what threat India can provide in a westpac scenario that is plausible
If you are just concerned about additional spying bases, well that's not so different than having more US military aircraft/ships operating from all the countries on the East coast.