It is quite correct imo to say that "prophecy" in the Bible (as well as in the Ancient Near East or Greek cultures) doesn't consist essentially or even mainly in predicting the future. It is another thing to make it a simple equivalent of "teaching". Immediate, extraordinary, supernatural revelation (i.e. inspiration received in states of ecstasy, trance, dreams, visions, or through divination methods) is always involved in prophecy -- even though in the "later prophets" of the OT this becomes more of a literary device than a real-life phenomenon. Early Christian "prophesying" is clearly distinguished from "teaching" (with one's own mind, as Paul puts it) as one of the Holy Spirit charismata or pneumatika.
It might be interesting to provide the exact context (and especially the NT "prooftexts") of the WT references to its "prophetic" activity. I wouldn't be surprised if they use the same texts, sometimes to refer to a "spiritual gift" that (they say) doesn't exist anymore, sometimes to an activity that still exists. (For instance, quoting 1 Corinthians 11:4 about a woman wearing a headscarf for prophesying -- which is supposed not to happen anymore -- and applying it to a "sister" teaching).