It's also kind of neat as a financial MAD instrument, because China obviously can't just get everyone to go into their brokerage and market sell a trillion in USTs so they get a lever to pressure the US with but they can't go nuclear without also vaporising their own value. So it works as a melting ice block on which diplomacy is forced on both sides.
The death of the UST as a reserve instrument would be a catastrophically bad loss, the only silver lining is that the melting ice block might still be enough by the end of this admin that the new admin might have enough to stand on to rebuild it should they realise the value of it.