Under this definition, faith can be a path (or perhaps the only path) to new or prevoiusly undiscovered truth. For example to prove P = NP (or P != NP) one must first believe that such a proof exists and then act on that belief in search of a proof.
You are right though in that it’s a stretch to call faith a “reliable” source of truth. For every truth that is believed and acted upon there are far more falsehoods to believe and act upon, some of which are really popular.