Nope, not a lie. You were doing the Origen of Alexandria thing, trying to treat God's Word like man's philosophy, creating allegories in The Word where there isn't one. I'll break it down for other brethren here that need to understand your false rhetoric...
You stated, and I quote:
The book of Revelation is a revelation of what occurred "before the foundation of the world" (just like "the Lamb slain")--which throughout history is only revealed. The book of Revelation is the final word, a wrap-up of things to be revealed--except for "the mystery of God would be finished as He declared to His servants the prophets." Which is to say, those things that were sealed during the history of the world while most things were being revealed--only the revelation of those things that were sealed would be the "finish."
Even with your very first statement where you claim Christ's Book of Revelation is about events that ALREADY occurred 'before the foundation of the world', you attempt to throw Revelation BACKWARDS IN TIME when the majority of its written events are actually for the VERY END OF THIS WORLD. And you try to use that "the Lamb slain" phrase to do that with, which is trying to create an allegory for Revelation that does NOT exist. Why do I say that? Simple, because the Book of Revelation is Christ Jesus' Book of Revelation that He gave through His servant John. It is NOT John's revelation. And Revelation 1 specifically tells us it is given to Christ's Church about events soon to happen, meaning future to Apostle John's day.
Then your next statement is really wild... that those things sealed during the history of the world while most things were being revealed, is like can't make up your mind, either they have been sealed until Christ's giving of His Revelation with opening the Seals, like it shows as written in Revelation 5 & 6, or they are still sealed today and won't be unsealed until your "finish" idea.
So it's not that difficult to see how you chop up Christ's Book of Revelation to create confusion.