Yes, you need actual presets to use presetFallback, otherwise the “fallback” is to load the effect and palette if you specified them and choose a random effect if you have not.
The idea for JSON remote was to make it easy for users to customize their remotes not necessarily to deliver a fully configured remote. Because I can’t possibly know what presets you’ll have.
But read the documentation for JSON remote. There is a tips section that discusses putting presets in blocks (by id) and setting up buttons to step through those.