Sorry, you don’t get to decide who is a Christian and who isn’t. Vanity is a deadly sin.
Which John? Not John the Apostle. .
And the Book of Revelation was questioned by many early historians, including Eusebius. Some church’s exclude it from their canonical text
Doubts resurfaced during the 16th-century
Protestant Reformation.
Martin Luther called Revelation "neither apostolic nor prophetic" in the 1522 preface to his translation of the New Testament.
Huldrych Zwingli labelled it "not a book of the Bible",
and it was the only New Testament book on which John Calvin did not write a commentary.
As of 2015 Revelation remains the only New Testament book not read in the Divine Liturgy of the Eastern Orthodox Church,