OK It sounds like there’s only one metric we can use to evaluate how much China pollutes.
The metric is widely used by various academics, government agencies and independent organizations. We have no better metric and that metric says that China doesn’t pollute that much.
That leaves 2 possibilities; the metric actually provides no information at all or it still provides some information.
If it provides no information AND we don’t have anything that does (ie a better metric) that means we literally have absolutely no information at all about how much China pollutes at all. That means we can’t make any intelligent claims about how much China pollutes or how much they’re fudging the number because there’s no comparison to make.
If it does provide some information we’re left with a situation where all of the imperfect information supports the claim that China doesn’t pollute much.
Either way, the evidence as you’ve classified it, doesn’t support the claim that China is, “one of the planet’s most polluting countries,” which was the original claim of this thread. It is, by definition, a baseless conjecture.