Parmandur
Book-Friend, he/him
I think the sheer epic scale of the change isn't clear to a lot of people. We aren't talking about a city being 100 miles or 112 miles from another place, we are talking about continent size changes.Inaccurate distances (and contours) on historic maps is a real thing and even now maps need to be periodically updated for accuracy. faerun getting a bit more epic magical explanation fits the genre but isn't really necessary
For juat the Sword Coast region, leaving off the rest of Faerun:
In the 3E/4E material the Sword Coast region as defined in SCAG is 2.2 million square miles (approximately twice as large as India)
In the 1E/2E/5E material, the Sword Coast region is over 5 million square miles (just shy of Antarctica, the only country on Earth bigger than the Sword Coast region is Russia).
That means the land that disappears and comes back is about the size of Australia. Just for the Sword Coast.
That is an absurd change. Even and eapecially compared to ancient and Medieval knowledge of geography.