For those who want to read the lore themselves but have yet to play through the Dungeon to get any armor pieces, you can go to Collections, find the badge for Sundered Doctrine, and read the lore off the armor pieces there.
------------------------------------------------
I wasn't expecting myself to feel sorry for the Dread, but the lore from the dungeon armor succeeded in doing just that.
Yemiq and Selin, the two Subjugators from Dual Destiny, are revealed to have been made from a single Tormentor, and the Witness appears to have put a piece of itself into them, potentially a Dissenter, and even carved away the notion of becoming whole on their own once it sensed that developing in Selin.
In the chest piece, Keit'Ehr is confirmed to be the first Subjugator created - its first attempt to bend Light and Dark into form - though they are considered a failure by the Witness, who asked them to prove their existence by escaping death.
But the boots reveal the origins of the Grim are nothing but horrifying. A Dissenter spoke out against the Witness, and the Witness responded by using twisted Light to split the Dissenter into the first of the Grim. The Grim are a single Dissenter's mind shattered into countless Grim, creatures of instinct who flock together in an attempt to find the connection between them, all of them connected.
Us killing each Grim doesn't help matters, either.
The Bond then shows us what happened to a Psion name Aemn when they were reshaped into one of the Dread. The process was so painful that Aemn escapes into a mindscape, while her body is reshaped into a Dread, the Dread manifesting as a shadow in her mind.
Other sections of the lore entries reveal what the Witness was doing to the Traveler after it successfully entered it during Lightfall. It turns out the inside of the Traveler was a place of pure potential, undefined and without shape until the Witness touched down and the mountains and soil formed within the Traveler, all before it set to work carving the Traveler's flesh open.
-----------------------------
Then there is the reason why Kerrev led his group of Dread into Rhulk's Pyramid. Without the Witness' control, each of the Dread in the Future Proof lore has a stated intent about why they are there, a unified purpose to make themselves anew. For now, we don't know what they hoped to find in Rhulk's Pyramid, but I can't help but feel sorry for them, even with the threat they might pose if they found what they wanted.
As for what Rhulk was doing with the Worms, we see corpses of much smaller Worm Gods the further we go down, embedded into the architecture as though they died while trying to burrow their way out. I've even seen it speculated that the dungeon might hint at Worms being able to freely interact with Light, or even convert Light and Dark if they so choose. Since a dissected Worm forms the symbol for the Dungeons, we're bound to learn more about the Worms from this Dungeon, and it will likely be tied to what the Dread were seeking.
The door in the Pyramid has finally been opened, and it was not what I was expecting.
[spoiler]
I saw promotional pictures of the room before, but I wasn't expecting it to be [i][b]Oryx's Chisel.[/b][/i] No wonder the Dread were drawn to it and wanted it for themselves. The Chisel created the Tablets of Ruin, and was used alongside Xivu Arath's Hammer and Savathun's Scalpel to craft the Dreadnaught; if the Dread got a hold of its power, they could "shape" themselves however they wished through the Taken power, which is still radiating from it.
Given this Dungeon happened to release with this Episode...Bungie is building towards something. Oryx's body was found in Ghosts of the Deep; in the main Episode, the Echo of Navigation is the Memory of Oryx as he was right after he killed Akka and claimed the Taken power; now, in the Sundered Doctrine dungeon, Oryx's Chisel is revealed to be locked up in Rhulk's Pyramid.
With the Episode's focus on us harnessing the Taken power, using poses and animations akin to the Subclasses, and when we were harnessing Strand, there are now two possibilities, though one is more like than the other. The first possibility is we're building up to Oryx's return. We have his body, we have an Echo with his memory, and we have the Chisel he used to craft the Tablets of Ruin. It is like pieces of a lost God are being brought together for its revival.
The other one, which I'm seeing talked about elsewhere, is that the Episode is building up to us gaining a Taken Subclass. I consider this one unlikely, despite all the visual evidence and what we've been doing this Episode, for a couple of reasons. But even if it is, one of those same reasons offers interesting lore and story implications going forward.
The first reason is gameplay and technical. We've gotten new Subclasses with major expansions, traditionally. Meanwhile, Heresy is an Episode that will be rotating out once Frontiers lands. We wouldn't be getting a new Subclass in an Episode, so it would need to be moved back to Frontiers, and there'd need to be a story reason for us to gain such a subclass in that Expansion. If that's the case, we can only wait for whenever they do the reveal for Frontiers.
The second reason i the hand that shaped the power. The lore and evidence indicate that Stasis was a Darkness power first shaped by Clovis Bray on Europa. We were the ones who first found Strand, and our hand was the one that shaped it into what it is. These shapes are set; even the Witness used Strand and Stasis in the forms they were first given when creating the Dread.
The power the Taken are derived from, "the ability to move worlds from one reality to another", was shaped by the Witness. If we were to take on that as a Subclass, even if we do so in a form distinctly our own, we'd have to reconcile with embracing a power first shaped and used by our greatest enemies. We are being taught the mindset needed to harness Taken energies for ourselves by Sloane (and we've demonstrated the means of absorbing and using Taken energy in the past), but harnessing and actively wielding it is another matter.
Especially from a story perspective. We managed to harness Stasis, and we were the ones who shaped Strand. What would the story implications be for us wielding the Taken power as a Subclass? What would even drive us to fully claim said power in Frontiers?[/spoiler]
It turns out I missed two lore entries because the Class Items have unique entries, not shared ones. Not only that, the Class Items are named for the origins of the Dread they discuss.
Titans have the Attendant's Mark; Hunters have the Husk's Cloak; Warlocks have the Weaver's Bond.
The Titan is about a Psion named Uolot, whose mind is split apart to create the Attendants, not unlike how a Dissenter's mind was split into pieces to forge the Grim. Uolot in particular was on Torobatl, their mind suspended in a moment on the day Torobatl fell to Xivu Arath and the Hive. During the process within the Witness' Monolith, it describes incomplete shapes of Uolot each with different emotions, and each of those shapes was "made whole" and slicked in Stasis.
Finally, the Hunter recounts the creation of the Husks. They were made from an Eliksni named Veskith of House Salvation, and it describes his mind being sliced into slivers during the process.
Something clicked when I read through the other two Class Item entries. It isn't just the Grim who are a product of a mind being carved into pieces; the Attendants, Weavers, and Husks were also created in the same fashion.
The Attendant and Grim entries seem to show how this is done - the Witness isolates the mind in specific moments and tethers them to Darkness, then manifests it through twisted Light into physical form. The Grim entry describes each moment as a "splintered impulse within the Word of Dissent"; the Attendant entry describes myriad shapes expressing different emotions, each a result of choices made, and how each moment was reshaped into an individual Attendant.
It is horrific, and it is no small wonder the Dread in the dungeon want a means to make themselves whole, make themselves anew. All of them are pieces of individuals whose minds were carved apart by the Witness and put into the bodies of the Dread, and, without the Witness' influence, they are trying to make themselves whole now that each one is coming into their own identities. The Grim are the exception, and it is likely because they were made from a Dissenter, not a former loyalist of the Witness.