Somewhat nice theory. I don't think OP lead to anything as whirpool being portals to other universes. But the rest seems plausible. Except the fact that he would be Luffy's worst/strongest foe.
Not other Universe, but basically Second Reality
Imagine One Piece World as a Coin, there are Two Sides to it, Two Stories
Roger's words to Turn World Upside Down
Oda drawing Old SHs in Two Timelines
Luffy saying "Dream within a Dream"
Everything in One Piece is Split in Two
One-Eye Hints referencing Pirates switching Decks on Ship
Dawn References
There are a Lot
But basically, there are Two Stories in One Piece
When we finally reach the Ending, we will witness which Parts of Story will remain & which will turn out to be "Lies"
Basically what Narrator said about the Book "Brag Men" summarizes the Story
And just like Usopp's Lies turn in Reality, can we really consider them Lies?
In other words, you could say that the Changes Luffy is causing in the World are what Remains, but how He achieved them are Completely Fake
Thriller Bark is Mini-Version of entire Story from Start to Finish
And Most Important Scene came at the End, when Zoro said "Nothing Happened"
It was Foreshadowing that when Dawn comes, you will realize that those words were referencing the Story & not Zoro