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?
If you want to use diamonds as an example then de beers basically controlled the diamond market for a long time.
They maintain an artificially high price through the restriction of supply although they recently lost control and the monopoly.