Should we be worried? Should we trade our BTC now for other coin like ETH?
Hundred times NO. Why the fact that most Bitcoins are mined now in China should be a problem? Most diamonds are mined in Central and Southern Africa and how exactly this affects the valuableness of diamonds?
That's not quite the same. Once real diamonds are mined and sold they don't have a connection to the mine anymore. That's not quite the case with Bitcoins. Bitcoins depend on miners even after they are mined.