I can certainly agree that there is no evidence to suggest that China is "one of the most polluting countries in the world". I haven't seen a shred of evidence to support that claim. It is entirely baseless.
On the other hand, the claim that China's per capita pollution is lower than that of most industrialized nations is supported by evidence. It is the best evidence we have too, unless you've discovered a better metric in the last few days.
A claim that imperfect evidence is equivalent to no evidence is baseless and will lead to erroneous conclusions.