Sounds like a pretty standard warscythe. Things normally take someone like a necron lord to lift them, I doubt a primarch would have that much trouble.
I don't think the callidus temple would have too much trouble getting phase swords if some shady necron was making deals on the side.
I also think the Deceiver absorbing the sword story is still perfectly canon, since shards are capable of going rogue. And really, if a Deceiver shard wanted to impersonate a terran noble, who would know? Except for the assassin. Right before she died.
Nonsense is our Salvation