https://www.dailydot.com/parsec/alien-covenant-disturbing-sexuality/Greetings. The above-linked article is a nice primer that looks at the disturbing sexuality explored both subtextually and textually throughout the franchise and how Covenant contextualizes this theme.
Now, for those that subscribe to the interpretation that David did
not explicitly create the familiar star beast and is not ultimately responsible for its design, life-cycle, etc, this is valid insofar that he's an unreliable narrator and full of egotism and grandiosity as a creator; he gets the author of Ozymandias wrong and more ironically lacks the self-awareness to recognize how the poem pertains to the inevitable downfall of kings and rulers.
Now Ridley is explicit about David being the designer and maker of the creature, yes, but Ridley also insists on Deckard being a replicant in Blade Runner. Now his view is valid and can be supported by the film but so can the contrary. Covenant is very much the same given that the accelerant is an ancient virus that pre-existed David's machinations. I certainly think it's valid that even the
engineers are not the progenitors of this virus and simply came upon it, wielded it with varying success but ultimately were destroyed by it.
David has an advantage in that he's synthetic and super intelligent and thus can wield the technology without the fear of being destroyed by it (thus far, anyway...), so he can unlock its secrets and blueprints more than the engineers ever could. However, one note is off, David's programming is unstable, and his "protomorph" is not quite the biomechanical beast nor is the life cycle he engineered from his crossbreeding experiments in line with the classic life cycle we know. So, it's just as valid to make the inference that the star beast has existed in its original form at some point before it was atomised/liquified, etc, as the tarry accelerant (black goop), for whatever reason. How it originally came to be and where it ultimately comes from remains a mystery.
On the other hand, David as the creator is another valid inference given how resolutely evocative it is of human sex organs. It's a walking, murderous, drooling dong. David's sexual hangups have been touched on by the artist Matt Hatton when he describes his pathos, indeed, David is built to be so close to a human yet cannot procreate; he can experience a simulacrum of human feelings such as love, etc, but cannot exhibit their function for mating. How does an increasingly unstable and satanic A.I. compensate for such conflict and, well, penis envy? Why... you create an organism that is a violent perversion of human reproduction, of course. The facehugger itself is two adult hands fused, a vagina and a phallus and literally rapes the host, before providing it oxygen. This thing is adapted quite wonderfully to human mammals. Themes of cold technology/A.I., sexuality, death and their fusion and transfiguration is something H.R. Giger explored throughout his art and a lot of the masterpieces he painted were visions of the future, not the ancient past. So David as creator has thematic merit and should not be dismissed without some careful consideration of Giger's themes in his body of work.
To whatever view you subscribe to is fine by me and makes the prequels rewatchable, even if we don't get a third installment (I'd love to see it wrapped and how much further the David character can sink into madness.)
Cheers for reading!
UPDATE:
Far meatier exposition of the sexual perversion of the franchise (sans the prequels) right here:
https://plotandtheme.com/2016/05/18/the-xenomorph-and-the-perversion-of-sex-in-alien/comment-page-1/#comment-25294