There's nowhere in the code that defaults a name to "Earth".
In the /upsert body, config.msv.mission is required and generally should remain the same as the top level mission (it's disabled in the Initial Tab but still can be changed programmatically here). Changing it would change the MMGIS page name as well as point to a different path in Missions/{mission} in case you're using an local/relative-to-Missions-folder paths in the configuration.
See #329
This is intended. Passing {mission: "string", config: {}} to /upsert will bump to the next available version number with the contents of config. Passing {mission: "string", version: number} will bump to the next available version number with the contents of the mission's previous configuration object versioned version.
It's true that the configuration validator is not complete. Most, if not all, of its validations happen for the layers.