cordova buildConfig not configuring Xcode project?

Question

I'm building my cordova-ios project using "--buildConfig=conf/ios/build.json", with that build.json having:

{
"ios": {
    "debug": {
        "codeSignIdentity": "iPhone Developer",
        "developmentTeam": "...",
        "packageType": "development",
        "automaticProvisioning": true,
        "buildFlag": [
            "EMBEDDED_CONTENT_CONTAINS_SWIFT=YES",
            "ALWAYS_EMBED_SWIFT_STANDARD_LIBRARIES=NO",
            "LD_RUNPATH_SEARCH_PATHS=\"@executable_path/Frameworks\"",
            "ENABLE_BITCODE=NO",
            "SWIFT_VERSION=5.0",
            "GCC_NO_COMMON_BLOCKS=NO"
        ]
    },
    "release": {
        "codeSignIdentity": "iPhone Developer",
        "developmentTeam": "...",
        "packageType": "app-store",
        "automaticProvisioning": true,
        "buildFlag": [
            "EMBEDDED_CONTENT_CONTAINS_SWIFT=YES",
            "ALWAYS_EMBED_SWIFT_STANDARD_LIBRARIES=NO",
            "LD_RUNPATH_SEARCH_PATHS=\"@executable_path/Frameworks\"",
            "SWIFT_VERSION=5.0",
            "GCC_NO_COMMON_BLOCKS=NO"
        ]
    }
}
}

The logging with my cordova build command (ionic cordova build ios -- --buildConfig=conf/ios/build.json --nosave) shows these settings are being applied, but when I open Xcode, these settings (at least the Swift version) don't seem to be set:

From my project's Build Settings, the Swift Language Version shows Unspecified.

My build works for development, but I'd also like the build to set the Xcode settings to simplify releasing the app for multiple developers. How can I get this working?