Yes, and no. Yes because you are vulnerable to supply chain disruption by illwilled countries. But illwilled countries that disrupt supply chains greatly incentivise others to diversify supply away from them.

China could have the monopoly of rare earth production and refinery for all of eternity. But because of their reaction towards all the us allies when the us increased tariffs, I don't expect them to be relevant enough to disrupt markets with rare earths sanctions in 10-20 years.