Whenever you have a large share in something, you can always use that dominant position to threaten the system. However, I don't think that China or any other large player would destroy Bitcoin because employing a huge level of resources to destroy the whole system would amount to the attempt of suicide. Considering the current global situation, decreasing GDP of China and trade war is something that they would like to focus instead of destroying Bitcoin.
Chinese blanket ban on Cryptocurrencies has been somewhat of strategic even as companies such as Bitmain have become some of the biggest crypto currencies in the world. China simply plans to harness the crypto wave in their favor and in full control of their central bank. In China, Tech companies and and blockchain itself are more shaped by the will of the government and than maybe in any other country. China's central bank has a more sophisticated understanding of how to leverage centralized blockchain than many other countries.
