Um, there are many MANY evangelicals that disagree with your sweeping assertion.
The bible is a collection of 66 books that were brought together and compiled into one volume long after John wrote the Revelations.
Further, John himself added to scripture after writing the book of Revelation, which is generally conceded to have been written while he was on the Isle of Patmos. It was long after John left Patmos that he wrote his first epistle. This fact standing alone would be sufficient to defeat the claim that revelation was closed and that man was enjoined from adding to scripture.
John was clearly talking about the Book of Revelations.
I could not care less what any man may say. God Himself is MORE than big enough to see to His revelation to mankind—the Bible. And Jesus, Who is God, is consistent, never changing. The words are His, whether they come through Moses or John or any of the other prophets and apostles.
Your mind will not be swayed, nor will mine be swayed to the man-made traditions of catholicism. My best wishes go to you.