I am just listening to the Corax Horus Heresy book, a selection of Novellas and short stories. There is a scene in Soulforge where Corax takes on 3 Defilers, 2 he destroys himself and the 3rd is destroyed by, I think a Thunderhawk, firing 3 missiles and pouring bolter fire into it.
Just before Corax enters the fight he sees as one defiler annihilates a squad of Raven Guard.
Now while the fight is not straightforward (Corax destroys the first easily, is then grabbed by the second, smashed into the ground several times and finally manages to get himself free before obliterating the Defiler) this feat does seem amazing even for a Primarch.
Is Corax known for being one of the strongest primarchs? I always thought his ability came from his speed and stealth. Do any of the source materials (including stat lines and game rules) suggest that Corax is capable of this kind of feat?