No. I'm saying when your application language is also your database or your operating environment [or for some other reasons], you don't need a configuration format.
The reason configuration file [formats] exist is because many programs are configurable and programmers are too lazy (or are not specified to, take your pick) to build a configuration tool [that has all their needs]. Configuration files are inferior in every way to an integrated and well-thought-out configuration process except that they may be easier to build and use in less ideal environments.
JSON is a fine format for interchange, and even persistence (i.e. to store configuration) but as a "configuration file" that people are expected to edit in their own way it is lacking, and that's why there are things like YAML and TOML and a million other things.
The reason configuration file [formats] exist is because many programs are configurable and programmers are too lazy (or are not specified to, take your pick) to build a configuration tool [that has all their needs]. Configuration files are inferior in every way to an integrated and well-thought-out configuration process except that they may be easier to build and use in less ideal environments.
JSON is a fine format for interchange, and even persistence (i.e. to store configuration) but as a "configuration file" that people are expected to edit in their own way it is lacking, and that's why there are things like YAML and TOML and a million other things.