useBabelConfig on fresh ember-app doesn't work

[ctjhoa]

Reproduction steps

• git clone https://github.com/ctjhoa/ember-use-babel-config-issue.git
• cd ember-use-babel-config-issue
• npm start
• Go to http://localhost:4200/
• You will end up with something like that
  

First investigation

Adding

    'ember-cli-babel': {
      useBabelConfig: true,
+     includeExternalHelpers: true
    }

in ember-cli-build.js seems to solve the helpers issue. However its not something documented as required.
Then you hit another error

This feature looks broken or lacks of documentation.

[NullVoxPopuli]

I'm experiencing the same thing. no matter my changes to a .babelrc.js file, even though it is loaded, my build output does not change at all.

Adding:

+     includeExternalHelpers: true

Did not change anything in my app's output