China accounting for a majority of production in an industry doesn't prevent the US from sanctioning China; if anything, it encourages the US to play on the fear of Chinese monopoly, which leads to even more sanctions. The reason is the same, ironically, on both sides - it's to force the domestic industry to diversify their supply lines and dependencies. Politics dictate economics and always have.
Also, to bargain, you have to have the right leverage. The problem with China's bargaining power vis-a-vis the West is that the West historically owned the high technology, while China just owned the labor and infrastructure. The latter cannot function without the former, but the former can function without the latter, since the West can take their technology to, say, India or Vietnam or Indonesia, and manufacture there.
This isn't to say those countries can fully replace China, but rather that scarcity is a natural law. If what you own is scarce (and high technologies like EUV are scarce), then you have more leverage. By contrast, if what you own is abundant (and labor & infrastructure are abundant), then you have less leverage. If China was the only major source of labor and infrastructure in the world, the West wouldn't dare to sanction China; but because of the pyramid effect in which there are much more competitors at China's level, than at the West's, the West believes it has the bargaining advantage and thus, the "right" to sanction China.
In other words, they are trying to show China how "abundant" labor and infrastructure is - by forcing it out of China and in doing so, reducing China's leverage.
The proper response is to show the West that their own "scarce resource" isn't nearly as scarce as they think - by developing alternatives to Western technology that, essentially, reduces the scarcity of high technology and thus Western leverage.
Well, a couple of points...
1. West
is not US.
US technology is not Western technology. I understand in US you are used to consider the terms equivalent, but in reality they are not. For instance Germany, but also Switzerland, France, etc all sell to China very high tech products and tools: airplanes, industrial robots, a very wide range of precision machinery, advanced tools in optics / lasers, etc. And guess what? They
will continue to do so, even if US does not like it.
Real advanced US technology that China needs and for which there is not any alternative, nowadays is mainly in semiconductor design and manufacturing, and maybe very few and specifics other niches. But even in semiconductors, US is desperately trying to force Europe and Japan to align, otherwise even here US alone can hardly slow down China....even less stop it.
2. In 2022 China is no more
just the Factory of the World
If you
still think that China is the factory of the world, you are more or less a decade late at the party. Technology in China is already world class today in many many fields, from renewable energy (included nuclear) to transportation, from construction to e-commerce and I even don't mention NEV cars, where China is at the forefront, by far.
And above all this China has
also the full supply chain. And this is not a small detail. When China will finally successfully localize chips, US will remain without banning ammo....and so it will switch weapon: close market for Chinese firms (Xinjiang style), financial war...and I hope not, but I would not be surprised at all, even a real war, better if fought by a proxy...like Taiwan, for instance.