Well, of course Revelation has always been regarded as a book of prophecy. The question is how to apply the prophecy.
The whole structure of the Book of Revelation is designed to show that “history repeats itself” in the history of the Church, including in the history of the Jewish people. That’s why the book is constantly describing events, stopping, and going back to the beginning and describing them over again. This is called “recapitulation,” and there’s nowhere else in the Bible that you get as much of it. That’s also why Revelation is full of quotes and references to Ezekiel, Daniel, Habakkuk, and many other Biblical texts, as well as stuff in John’s Gospel and letters. In some ways, you’ve heard all this stuff already.
And yes, the Book of Revelation was directly addressed to a bunch of Christians in Asia Minor, a long time ago. But yes, the stuff that is talked about is stuff that tends to happen over and over again in the history of the Church. As John says in his letters, there are tons of Antichrists in the world. As described in the Revelation letters to the seven churches, there are also tons of Laodiceans and Jezabels and so forth, always and everywhere. It is endlessly relevant, until the end of the world.
(Pretending that each letter to each church represents an age of history is silly, though. Obviously all those churches really existed and had really quite different personalities all at one time, so why claim that the same thing is not true of all sorts of parishes and dioceses and individuals today? Some early Christians like Augustine did believe in “seven ages of history,” but they placed all of them except number seven in the OT times! So no, that wasn’t how they interpreted the seven church letters. Some people have tried to connect the seven letters to Paul’s letters, but that doesn’t work either, except as John referencing Paul by writing letters to churches. Still pretty farfetched, though, since bishops did write letters to churches, and John was a bishop so he wrote letters. Using them in a book as a literary frame was what was different.)
However, it’s also true that the Book of Revelation does also talk about what will happen at the very end of time, in the very last and worst persecution of all the persecutions the Church has to suffer throughout history. It’s just that most of it is also applicable to lesser persecutions and smaller troubles.
The point is to stay watchful and ready, because we will never know the day or the hour, and Jesus has already warned us that He will come like a thief in the night. It’s a lot easier, and more sensible, to do what He says: stay ready, spread His Word, and do good without fear.
And finally, the other point is that in the end God wins, and that we can also win and live forever in glory, if we persevere and do His will. That should make us all happy; and that’s why Revelation is full of praise and singing and music.
As for what Vatican II said about it, “Dei verbum” doesn’t make direct pronouncements about particular books of Scripture; that was the Council of Trent, which specifically confirmed the Canon that was in use by the Catholic Church. Chapter 5, section 20 of “Dei verbum” does say:
"Besides the four Gospels, the canon of the New Testament also contains the epistles of St. Paul and other apostolic writings, composed under the inspiration of the Holy Spirit, by which, according to the wise plan of God, those matters which concern Christ the Lord are confirmed, His true teaching is more and more fully stated, the saving power of the divine work of Christ is preached, the story is told of the beginnings of the Church and its marvelous growth, and its glorious fulfillment is foretold.
“For the Lord Jesus was with His apostles as He had promised (see Matt. 28:20) and sent them the advocate Spirit who would lead them into the fullness of truth (see John 16:13).”
