Even if the criticism is fair, it's still whataboutism. I agree with you that countries other than China have done bad things, including post-WWII, but not that it in any way justifies turning the streets of Taipei into a warzone.

I wouldn't unconditionally agree that "the US is a much more egregious international actor than China". I'd use a more neutral descriptor than "egregious", maybe "militaristic". Following the rule of "might makes right", as you point out, the US more or less became the self-appointed world police after WWII. That's inherently going to involve unpopular decisions and occasional abuse of power, but it's a fundamentally different relationship with the world than pure assertion of first-party interests. The ultimate goal of post-WWII American foreign policy has been to ensure that the rest of the world remains stable and open enough for reliable trade, from which China has also benefited tremendously.

US as world police is a mixed bag, but it is what it is. No one outside the US is really complaining that America bears the cost of its navy protecting international trade routes, for example. I'm as harsh a critic of certain US actions and policies as anyone, but modern American hegemony doesn't resemble the prior centuries of great powers running amok. The US today doesn't invade innocent countries for the purpose of stealing their land and resources or enslaving their people.

The concerns about China aren't limited to its past military actions, but also its domestic policies and stated future goals. For better or worse, China's domestic policies are quite illiberal relative to American values. This alone precludes China from being considered a clear ally of the US, and informs perceptions of what a hypothetical Chinese-led world order might look like. China gets to play the "what about America" card because the US is still generally invested in globalism, but how China might behave in a power vacuum created by a US shift to isolationism remains speculative.