Doesn’t this assume the existence of a strong fourth estate and/or an executive branch, able and willing to investigate leaks?

There are ways to at least partially inoculate against leaks; regulatory capture and elimination of accountability, quid pro quo journalism, “fact checking”-driven censorship, or just simply positioning yourself politically so that the responsible entities don’t want to investigate.

Anything left over can be written off as a smear job, a conspiracy theory, etc.