There's no reason to believe that the xeno varieties we know and love couldn't have or didn't exist before David played around with his tissue remixes on Planet 4
Actually, there is very good reason to believe they didn't exist before David. It's what Covenant said, and it's what Ridley Scott fully intends, and since it is canon, we must roll with it.
Sure man, live it and breath it. Ride the Tiger! I assure you friend, I am in no way calling into question your fanhood. I'm just offering my counter interpretation of what I see in the film and how that would most reasonably fit in with an inclusive combined AvP universe encompassing Alien as well as Predator.
It sounds like you might practice belief in irreconcilably exclusive universes in which only the three Ridley Scott films are valid members, and that's cool. The way I interpret the essence of any given story is by accounting for all of its different iterations, and then comparing where the details of those various iterations are either similar or dissimilar. But perhaps, in your interpretation, there's more of a hierarchical structure in which there is only one true vision with one true creator rendering all others moot.
I guess what I'm trying to say is that, figuratively, all the different orange varieties are oranges, and if I'm understanding you correctly, you're saying that one
variety of orange is more orange than all the other varieties of oranges, and thus, the rest of the varieties cannot therefore truly be oranges.
Or, more to the point, using Blade Runner as an example, I would contend that all 7 versions of Blade Runner are collectively Blade Runner, and further
that the scripts, the novelization, the comic adaptation, the original Philip K Dick novel, (both the first version set in 1992 & the later revision set in 2021
), the other PKD stories connected to "Do Androids Dream..." like "We Can Build You" and "The Little Black Box", as well as the audiobook productions, and also the radio play adaptation, are all aspects of that same story that together makes up, in my mind, that which is "Blade Runner".
Conversely, you may perhaps believe that the 2007 "Final Cut" is the one and only true Blade Runner and that all other versions, perhaps, are merely sickening pretenders to the throne. And to that I unironically say, right on man, love what you love any way you want to. I ain't ever gonna take that from you.
...and by the way, that’s not eeeeeven calling into account the KW Jeter Novel sequel series, the comic prequel Ashes to Ashes, or the sidequel video games or the ongoing Blade Runner 2019 comic, or 2049 or the short films.. whew lemme catch my breath. I never said it was a better way, I only say it’s more exhausting.
Lawdy lawdy, guess who needs a 40’...
But yeah, I am genuinely this big an “Ass Burger”, great with numbers and obsessive hobbies, bad on human simulation skills.