Just because the biggest bitcoin 'mining farm' is in china doesn't meant china can controlling bitcoin.
But yes, china has the cheap electricity cost, that's why they have the 'power' about bitcoin, not controlling bitcoin.
As we know bitcoin is decentralisation, which means no one or no organisation or no country can controlling bitcoin.
These are empty words, there is no absolute decentralization. The Blockchain itself is an example of utmost centralization since there can be just one authentic instance of it. Perhaps, only total chaos comes close enough to the idea of absolute decentralization, though even this is debatable. The homespun truth is that right now Bitcoin mining is heavily centralized. Whether this would count as control over Bitcoin is debatable too, but this doesn't in the least undermine the possibility of the Chinese miners to essentially shut down Bitcoin if they ever choose so...
If you don't see that, you'd better open your eyes