This is unclear in Connect Document about the limitation in Custom Editor URL.
Url context parameters are not supported for custom editor url. This is not consistent to other url value we can use for connect addon. Currently Navigation API is the only alternative for editor to determine contentId etc context for page. This needs to be either documented clearly or improved other wise.
In V3 custom param is sent to addon url using GET, but in V5 it is missing, and it is a regression from existing feature.

For example:

"editor": {
          "url": "/my-macro-editor?content_id={content.id}"
}

Expected:
editor will be called using GET /my-macro-editor?content_id=<some real id>

Actual:
editor is called using GET /my-macro-editor?content_id=

Workaround

Call AP.navigator.getLocation(...) to obtain the content ID.