China processes ~90% of rare earth raw materials into actual rare earths

Then onshore the processing to Japan, other countries like Australia can provide the ores

only because nobody else bothered to build processing plants for the low demand minerals.

it is trivial to build and these minerals can be found everywhere

You are delusional if you think it's trivial.

This.

Yes, 'rare earths aren't rare,' and I hear that, and then I also hear that everyone is screwed if China won't sell theirs.

It can't be both. The key reasons I've heard for China owning this market are a) they have large deposits, b) they heavily invested for decades, and c) they aggressively dump and undercut in an anticompetitive fashion to ensure they keep the market cornered.

Seems like the only way out of this is to stop being religiously opposed to state subsidies in an industry of clear national security importance, combined with maybe a Herbert Dow-style jiu-jitsu move of countering any dumping by stockpiling and then re-selling the below-market product.