Indeed, this is so much the case that they found the very same legion: The Black Legion. Both are amongst the highest-ranked members of the Arch Traitor's legion, and both declare their primarch a failure after their respective Heresies, going on to reform their legion into a new, general traitor legion. Dornian Heresy Sigsimund of the Imperial Fists is largely the equivilent to Horus Heresy Abaddon.In this case, the substitution is narrative. Both are almost unabashedly heroic, both have prophetic visions of the future, both have a great deal of love for their father the Emperor, and both sacrifice themselves in a clearly doomed battle against their respective Arch traitor. Dornian Heresy Konrad Curze fills largely the same role as Horus Heresy Sanguinius.This can be either from the perspective of the overall narrative, or simply the personalities of the involved characters.
Suspiciously Similar Substitute: On occasion, Dornian Heresy characters are very clear substitutes for Horus Heresy ones.
And, most shocking of all, Abbadon became a tactical genius! Lorgar chose to declare a holy war upon Chaos rather than siding with them. Ultramar was tricked into fighting the Alpha Legion and Word Bearers, resulting in them becoming a third power, meaning that they were no longer held by the rules of the Imperium and began to tinker with their technology. After the Heresy, the Legions were never broken up to make sure they could stay strong and root out traitors within their ranks. Angron had Horus and the Emperor side with him during the slave uprising on his world, resulting in him removing the canonical Butcher's Nails in his warriors. The Emperor sided with Magnus during the Council of Nikea, and Magnus privately requested that the Emperor perform the soul-binding ritual on him and the Thousand Sons to protect them from the influence of Chaos, meaning that the Thousand Sons gained the power to banish and in some cases even outright destroy daemons.
There is still at least one surviving loyalist primarch whose location is, to an extent, known, and there are fewer true traitors.
And after the Council of Nikea, Magnus privately approached the Emperor with a request to perform the soul-binding ritual on him and the Thousand Sons, both as a protective measure against Chaos and to assure the Imperium of his legion's loyalties. Here, Magnus' loss of one eye was attributed to a demon of Tzeentch taking out one of his eyes as an infant before his incubation pod crashed on Prospero, his missing eye being replaced with an "ugly welt of scar tissue". Disabled in the Adaptation: Canon Magnus is one-eyed, though how he got that way is Depending on the Writer.