Other way around, the Dreamlands are not apart of the Mansus, they never have been. It used to be that the Woods covered the Dreamlands, it no longer doing so is why the Worms are infesting the Dreamlands as they can see the dreamers. And your thinking to logically, the path forged to Harmony could be build sideways, or from above the manuses, as viewed from the mansus proper. It very much does not have to make logical since to exist alongside the mansus yet be fully separate.
The Mansus appears to be a piramid, but the way it was described from the top, or - more relevantly - from a more knowledgable position of late game Velelvet, as well as BirdBodhisattva somewhere in the comment way back, the Mansus is described differently:
The Mansus feels like… a sphere, or maybe a cylinder, or perhaps an endless sea of concentric rings. Or maybe…
Still, as your hoof steps on the firm Mansus stone, you understand that… that Glory is the center.
Maybe the Mansus, or perhaps the entire world, is an inverted sphere. And if that is the case, then Glory is at its very center.
Maybe all of reality is a cylinder. Layered in levels, with the Mansus being the innermost and Wake the outermost. And everything spins around the axis that is Glory.
Because here, you finally understand. You finally understand that to go up is to go towards Glory. To go down is to move away from it. And that which Glory's light cannot reach is nothing. The places where Glory does not shine is Nowhere.
I do not believe it is possible to approach the Glory sideways from the Mansus, not anymore than it is possible to approach the center of a sphere by moving just tangentially; and it makes no more sense to approach the Glory from the above than it makes sense to reach a sphere's center by moving outwards.
You can be above the Mansus, even closer to Glory than the Three-Valved Door is, but that is not really "separate".
It doesn't
necessarily means that everything has to intersect the Mansus, but the Dreamlands were pretty consistently "away" from the Glory and its light.
I can believe that
maybe, Harmony is kin to Glory. After all, from the description of the zeroth level of Knock, the most fundamental, the most basic of its lesson is that the Mansus is a different World you travel in your dreams:
-Level 0: You understand that there are other Worlds, and secret paths between them. But the only one you know is the World in your dream, the Mansus, and perhaps that is the only World that matters. (Allows access to the Mansus)
So, could it be that like the Glory is the shining core of the World called Mansus, Harmony is the shining core of World ponies call "Equestria"? Lesser, not nearly as luminescent, perhaps even subservient, but kin, the native power of the living world?
Although, by all indications, while the Harmony can be "native", the ponies are not if such distinction between the Mansus and "Equestria" makes sense. We know that before horn, wing or might, they all once originated in the Blank Plains, in the Mansus.
Perhaps, when we say that "the Wake" is "Equestria", we are even making a mistake. Perhaps, "Equestria" is not the only World that the Mansus have caught in its Wake? After all, we do know that the Daughter of Axes, if only she could unchain herself, would have spoken so:
[ ] She spoke about this world, Equestria, and the many other worlds that ponykind knows to exist, and the secret passages that connect them. Figuratively, when referring to other countries, and literally, speaking about far away realms that most ponies believe to be only fairy tales. (KNOCK is the principle of openings, and of finding hidden passages and portals. It entails secrets that both locksmiths and burglars share, even if they do not realize it.)
"Far away realms" do not speak of me as some realm on the other side of the darkness of the night skies. If it were so, the ponies would not have heard of them, and even fairy tales of those Worlds would not have existed.
It is a far stretch, I don't really believe in this "kinship", but it is an entirely valid view of the lore given. Like, maybe it's an early installment weirdness, there's a question of how literally we should read lore written in the very first days of the quest, but it is not
opposed by anything.
Returning to Harmony, I do not believe equating it to Glory makes sense. Technically, it is possible: all of that were biased perspectives of in universe characters, except maybe Knock 0 description. Mistakes are not impossible.
...But they do not make sense to me. Not in this number, not in such severity.
