Why will China maintain the upper hand in the rare earth minerals market despite potential US-Ukraine agreements?

According to geological expert Viktor Nescarovsky, most analysts agree that even if the US and Ukraine reach a deal regarding rare earth minerals, China will still maintain the upper hand for one simple reason. While the transcript doesn't elaborate on this specific reason, the context suggests China's established dominance in the rare earth supply chain is difficult to challenge quickly. China currently controls a significant portion of global rare earth processing and production capabilities, giving them strategic leverage in this critical market despite diplomatic agreements between other nations.