“Palantir does not need to own the data or even have stewardship. They can extract, transform and exploit the metadata to build their own rich picture.”

Sorry, but this is full on into conspiracy theory here. Are we seriously arguing that Palantir are doing very much illegal analysis on air-gapped national security systems, and somehow exporting those and aggregating them?

The exact same concerns could be articulated for Google/AWS/Azure, but nobody does because they would quite rightly be called out as conspiracy theorists.