Not sure about other repositories, but with Google drive... you are copying a document into Moodle. (let's say you are using the File resource, as a teacher). You are not linking to a live version of the document inside the user's Google drive account.
Which seems very useful if the students ask to submit an a Google drive document as an assignment, as you do not whan them to continue editing it after the have submitted it. and the above "feature" is actually taking a snapshot of the Google drive document into Moodle's assignment activity.
Not sure if that is what you are looking for, but it is one common way we are using it.
Also, there is that new Moodle Google drive module I developed that enable the teacher to create and share a Google drive document from his own account with her/his students (link) which you already know of, and which seems to be more useful to your scenario, as far as I understand it.
Hope it helps