One human born Alien took out the entire Nostromo. One Space Jockey Alien would be TERRIFYING. I know its supposed to be the "Deacon" but thats just more horse shit to me. I'm done considering this new plot canon.
It can't be the "Deacon" unless the creature that infected the Space Jockey was also birthed from a human.

Biology of Parasite x Biology of Host = Biology of Alien
It can be assumed that the Space Jockey was simply infected by a Face Hugger.