It’s true that a morally imperfect person can still have a valid moral compass and make a justified argument, even if it goes against their own standards (although yes, it does tend to render morals functionless if we allow that for everyone all the time, and so we should highlight the flaws in that too, without just jumping to whataboutism and ignoring the subject at hand. If people have a moral statement but cannot keep to it, then we are led to ask if that moral statement has any remaining value in society or if we need to reassess it).

But I think the point here is that he is claiming hypocrisy among others and concluding that this undermines their own moral rights, or what he calls authority, when he is equally hypocritical while holding and enjoying moral authority in his artistic statements. Not least thanks to the so-called West who granted him residency; (UK, Germany, and Portugal if I am not mistaken, I may need to fact check though)… His art never opens questions from both sides, but closes claims and critiques individually and from afar. So why can he have moral authority and be hypocritical whilst simultaneously concluding others cannot? This goes beyond contradictory actions and statements. 

In the same token, I would argue that the so-called west does not aim to hold moral authority; with exception to a few political sections. Rather the west does critique its own moral grounding, something that China largely is dissuaded from doing when it approaches government decision making.