You ever heard of the unparalled invasion? Its a plausible Europeans conquer China scenario
It exists but isn't plausible. Japan did a biological warfare campaign against China in the 30s/40s and didn't win, why should Europeans win in even earlier decades?
Still begs the question of why not just dispose of the excess population in the Americas/Australia instead of seeking genocide/ethnic cleansing/mass murder on people who would otherwise make a good market for our products or cheap labour to make said products. Even the strongest American Indian groups were a lot less effort to brush away than an ethnic cleansing campaign in China might be.
Even Kenya-levels of white settlement would be hard to get in China, simply because you need to do something about the Chinese, and by "do something", I mean a violent and brutal ethnic cleansing campaign to allow Europeans to insert themselves. And that's pretty expensive for any would-be colonialist.