It is true that the Book of Revelation isn't milk for babes (1 Cor. 3:1-3). It is also true that someone doesn't need to understand its meaning to be truly converted to Christ. For, one must only understand "the principles of the doctrine of Christ" to be justified before God in Christ (Heb. 6:1, 1 Cor. 1:18). However, can we truly say that the Book of Revelation is something "other than" the Gospel?
"When nations are to perish in their sins,
It is in the Church the leprosy begins -
The Priest, whose office is with zeal sincere,
To watch the Fountain, and preserve it clear,
Carelessly nods and sleeps upon the brink,
While others poison what the flock must drink.
His unsuspecting sheep believe it pure,
And, tainted by the very means of cure,
Catch from each other a general rot.
Then Truth is hushed, that Heresy may preach,
And all is trash that Reason cannot reach."
- William Cowper
“The Revelation of Jesus Christ, which God gave unto him, to shew unto his servants things which must shortly come to pass; and he sent and signified it by his angel unto his servant John: Who bare record of the word of God, and of the Testimony of Jesus Christ, and of all things that he saw. Blessed is he that readeth, and they that hear the words of this prophecy, and keep those things which are written therein: for the time is at hand.” – Rev 1:1-3
“And they overcame him by the blood of the Lamb, and by the word of their Testimony; and they loved not their lives unto the death…And the dragon was wroth with the Woman, and went to make war with the remnant of her seed, which keep the commandments of God, and have the Testimony of Jesus Christ.” – Rev 12:11, 17 [Rev. 11:7]
“And I fell at his feet to worship him. And he said unto me, See thou do it not: I am thy fellowservant, and of thy brethren that have the Testimony of Jesus: worship God: for the Testimony of Jesus is the Spirit of prophecy.” – Rev 19:10