Wait, is this in the movies? Where is it said that the xenomorph were created by the engineers?
What I got from Covenant was that the alien/xenomorph was David's creation. He set loose the black liquid on the engineers home planet and started experimenting and evolving his creation with the wild life and then it all ended with the original xenomorph when the covenant ship landed and the human impregnation happened, which finally let David create the perfect organism and became a God or whatever.
If he's just duplicating what the engineers had already created then maybe I can stop hating the story. Need to rewatch asap!