Theory on the blood ravens (and gray knights) origins

Late to the party, I know. This is something I've been thinking of while replaying the dawn of war series.

What if the blood ravens are not an offshoot of the thousand sons, but instead are remnants of one of the two "lost" legions? Here's the key points I'm considering:

1. The two lost legions' fate is never made known

2. While the primarchs are known to be "lost to us", they aren't likely to have fallen to chaos, because the now-chaos legions' histories weren't removed (at least not entirely), while the two lost legions' histories were completely erased, and it happened before the heresy.

3. The Blood Ravens hold knowledge, collecting and preserving imperium relics above anything else

4. The Blood Ravens have, in Dawn of war Soulstorm, access to a team of Grey Knights. This is highly unusual, as most chapters aren't even allowed to know about Grey Knights' existence.

5. Malcador the Sigillite had a staff with a raven fixture at the top that very closely resembles the blood ravens symbol. In addition, Malcador sacrificed himself for the good of the imperium - which may be what the blood drop may symbollize

6. Malcador is at least once depicted as sitting on a throne with two skulls on either armrest, one marked with II, one marked with XI. This to most people implies that he had something to do with those two lost legions' erasure from history, but what if the two skulls being on a throne he sits on is symbollic of him also having taken charge of them after their primarchs were deemed failures?

7. Malcador's own lifelong goal was to retrieve and preserve relics of humanity's past, and knowledge.

8. Malcador basically created the Inquisition, the highly secretive organization that has no qualms about erasing things just to maintain secrecy about their operations.

With all this in mind, would it not make sense that Malcador might have erased all traces of the 2nd and 11th legions specifically to employe them as his own secret agents? One legion to fight chaos, as the emperor feared his own demise was at hand, one legion to continue the Sigillite's work, as Malcador likely suspected if the Emperor was to fall, he would also suffer the same fate.

Thus my theory: one of the two lost legions was repurposed to serve as Malcador's successors in purpose. In his honor they bear the raven of his staff and the blood drop symbolizing Malcador's sacrifice, and they continue his work with little regard for anything else. For the sake of clarity, let's say Blood Ravens are former 2nd legion and Grey Knights are former 11th legion (Could be the other way around). Both legions suffering the same fate of being erased from history and placed under secretive orders from Malcador would explain how and why they are allowed knowledge of the Grey Knights' existence and why Grey Knights might have aided them during the Kaurava campaign. (I know the inclusion of grey knights as a unit might have been pure gameplay but hey, they're there, might be a hint as opposed to just gameplay)

I know there are theories that they're dark angels descendants because dark angels chapter foundings aren't recorded, but dark angels chapters also work closely together and are weary of every other chapter - the blood ravens however (through flavor text in various wargear you can acquire in the game) seem to be making at least attempts at fraternizing with other chapters (e.g. made an axe to gift to the space wolves - they refused).

There are theories that they might be thousand sons because they have many psykers - but thousand sons also suffered mutations, which blood ravens don't exhibit.

Blood Ravens instead might have their own gene-seed quirk, something akin to zeal - as long as they have a clear goal, they'll pursue it to the exclusion of all else. In dawn of war 1, they refused to extract prior to the warp storm - they had a goal to complete even if it meant becoming trapped. In dark crusade, they had a goal to secure the planet because of the secrets therein - even if they had to kill loyal imperials for it. In soulstorm they fought to eliminate any potential threat to the imperium, even loyal imperials and sisters of battle - they were told to scour the system, and they set out to do it even if they ultimately lost. In dow2 they had to secure their recruiting worlds even while outnumbered and outgunned and with resistance from the local government. In chaos rising they had to once again secure their worlds even if it meant disobeying direct orders. In retribution the traitor blood ravens became focused on chaos worship - but it wasn't worship of Tzeentch, like a thousand sons descendant might turn to for more knowledge and secrets - it was to khorne: they wholeheartedly abandoned their search of knowledge and relics, only focusing on earning khorne's favor.

So their gene-seed quirk might not be the unusual amount of psykers - that may be a side effect too, or just a coincidence, but they seem to be much more driven by raw obsession - with anything they set their sights on doing: whether it's following their primary Malcador-given directive of finding and preserving relics (according to this theory), or with earning the favor of a chaos god, or anything else in between. Maybe it was this obssession that made their primarch a failure - the equivalent of an odd combination of ADD and fixation, where if he found something he wanted to do, he'd be completely distracted from whatever else he was meant to be doing. Where all the primarchs were meant to be military leaders and statesmen, this one may have been too unstable in his personality to be able to focus on either facet of his given role unless it happened to be something he wanted to do - and he may not have wanted that role, making it a failure of a primarch indeed.

Further evidence against the thousand sons connection is:

1. Guilliman told Cawl to only make primaris of the chapters that were not part of the heresy

2. Blood Ravens have primaris gene-seed available

Where the distinction may lie, is that Cawl interpreted Guilliman's orders in his own way - leading to the delay of the release of Primaris. We know Cawl had access to all twenty of the original gene-seed stock, and we know the two lost legions did not fall to chaos - Cawl may have interpreted the two lost legions to fit the criteria as well - which would mean that he may even have Primaris gene-seed for the Grey Knights.

As a tangent with the grey knights,. while the grey knights are stated to have been created specifically to combat chaos and they've never fallen to chaos, what if that was their gene-seed quirk? The grueling training the initiates go through may just be something that's required in order to properly integrate the gene-seed of one of those two lost legions. Maybe that's also why their primarch was a failure. He might have somehow become a Daemonhost, and as a result his gene-seed was more resistant to chaos, leading to the legion created from that gene-seed to be highly resistant themselves. That would probably be reason enough for a primarch to be deemed a failure. And if their primarch was a daemonhost, what better way to further obfuscate that than by state that they were made directly from the emperor's own gene-seed to erase that shame?

To summarize, I think perhaps while the two lost primarchs are indeed lost - dead or otherwise non-functional, their legions may have become the blood ravens and the grey knights, both under Malcador's control while he was alive, both given mandates by Malcador. The skulls on the throne and the raven-shaped staff being very reminiscent of the blood ravens' badge were the two things that led me down this rabbithole.

Thoughts? I know there's no confirmation, obviously, it's just a theory, but I think it better explains all the details we have about them, with all the context we have about who they can't be descended from and what gene-seed quirks they don't have and the sort of personality they exhibit.