What a weird influence campaign
No one is getting super rich by mining rare earths, since they aren't really particularly rare. Sure, the more the mining is concentrated in China the more (temporary) influence they'd be able to exert on supplies, but there would be a lot of better ways to gain leverage over western economies. Plus the more mining that happens in China the more of the pollution resulting from it that happens in China.
You'd think it would be a much better bang for the "economic warfare" buck to try to sabotage efforts to build new fabs in the US, or infrastructure in general...