The editorial actually very carefully (and rightfully) isn't arguing for 'let China do all the mining' (or even avoiding duplicating mining efforts). It clearly

The editorial actually very carefully (and rightfully) isn't arguing for 'let China do all the mining' (or even avoiding duplicating mining efforts). It clearly says so "But it would be unwise for the rest of the world to rely on just one country for the processing of critical minerals" (and logically the same would be true for mining). The editorial is arguing against trading blocs. In fact, it's arguing for some form of free trade. This benefits China in both that it is currently in a dominant position in terms of market and capacity, and also favors China in that it neutralizes one area where the US generally holds advantages - better soft power, and a being generally thought more favourably than China.