I think you argument would be a lot better, if you were more careful about discussing the difference between the things that are done by the government of a country, and the experience of people living in that country. Ordinary Chinese people are not imprisoning Uighurs in their living room, and ordinary Americans aren't dropping bombs on Yemen on the weekend, both would find that abhorrent, so when they hear their own country described through these activities it's jarring, but feel less discomfort describing the other country through reference to it's worst atrocities.
If we wanted to, but I think it's unnecessary for this conversation, we could compile a list for the terrible things that China and the US have done, and both list would be horrific.
There would be two significant differences between the two lists at the moment:
The US military is much more active outside its own claimed borders
The Chinese government is much more active suppressing speech and thought.
I do not believe these differences are due to any moral superiority on either side - that would be a rather remarkable claim.
The people run over by tanks in Tienanmen, arrested for political dissent in recent years aren't Americans, they are Chinese people pushing for a more open society, a desire for fairness is not an American quality it is a human one. As federal agents abduct protesters of the streets in Portland, it should be clear - abuse of power is not a Chinese failing, it's a human one. I think the there is a very good case that the difference between the lists of Chinese and American atrocities is simply a description of the differences in power and accountability of the two governments. There are plenty of good reasons to fear that both governments would like to expand their power and reduce accountability to look more like a hybrid of the worst of both.
Your last sentence takes something that's real - white racism and assumptions of cultural superiority, and elevates it to 'the real problem', I think you're close, but you've missed a bigger picture. A Chinese friend of mine told me about breaking in to hysterical laughter as a child when first hearing about white supremacy, a the story as she tells it now (ironically) is that her reaction was 'what idiots, don't they know the Chinese as the superior race!'
Identifying with a group is deliciously pleasurable, identifying with a nation, with it's flags and songs and strong military even more so, and puts us in a vulnerable position, in which powerful people can use that identification, to weave an overly simple myth about our country that blinds us to complexity. Free speech, ending military aggression won't kill China or America, but it will destroy the power and fortunes of some within those countries.
When we engage in tit for tat whataboutism in these forums, we are averting our eyes from the flaws in our own countries, and advancing the fortunes of the greediest and most destructive people in our societies.