And when a journalist receives a tip from a reliable source they can't open with their secure PDF tool, they are more likely to do what? Disregard the info, or open the PDF in an unsafe tool?

That's not an option. JBIG2 is objectively the best format for compressing black-and-white scanned images. The Adobe Acrobat software has an "optimize scanned PDF" feature that produces this format. It's not obscure at all.

That objectively best format that was banned in some areas due to replacing important numbers in accounting documents? But if it's the default in Acrobat, yeah, likely not obscure enough