My Alien Theory:
So Alien: Covenant was AWESOME! it totally quenched my thirst for new Alien universe expansion plus left the story current story open to head in a totally different and even more previous direction... let me explain...
David couldn't have created the Xenomorphs. The derelict in LV-426 with the chestbursted pilot was millions of years old when it was found in Alien, so the xenomorph or a variation of it existed long before David cooked one up in a lab on a distant planet.
What I think is happening is that while Weyland was obsessed with finding the formula to eternal life, David was obsessed with finding the Engineers and replicating their solution to the formula to eternal life and replicating it himself... xenomorphs.