I'm going to just point this out, the Deacon would be the proto-Xenomorph. The Deacon is the earliest one in the timeline and not the Covenant Xenomorph.
Not calling the Xenomorph in Covenant a proper Alien is simply being pedantic. Because if we do have to consider the Prequels as the origin, then this is it. This is the earliest the Alien exists in the timeline until the next film screws up the timeline more. There is no baseline in these films so being general about the design is fine.
What do I mean?
It spawns from an egg hosting a facehugger, it attaches and JOs down somebodies throat, out pops a bundle of gross, and it grows up to be a screaming skeleton with a penis head.
If our argument against it is the chestburster.., well the Runner starts formed and we have no idea if this is because it grew inside of its host or if that chestburster merely starts that way. We also got ALIENS which gives them arms, and even the Queen burster had developing
arms.So regardless something like this can happen as weird as it is. There is precedent that they don't always start as penis snakes with the Runner being the most developed.
And if our argument is the physical form, well as bad as the design is, there's also some minor precedent for it. We know the PredAlien will typically develop a more fleshy appearance taking on the added muscle of its host. It might not be out of the question for it to do that for a human. And we know that the carapace does develop over time. As boring as the design in Covenant is, we know they eventually gain more shell.
For all intents and purposes it is the Xenomorph, even if the showing isn't great it might as well be seeing as if it wasn't suposed to be we would've just stuck with a Deacon or Neo-morph.
In addition, if this is isn't supposed to be the proper Xenomorph then David has not created the Xenomorph. In Covenant he would've just made a passable attempt no different than the scientists in Alien:Resurrection. However if David did create the Xenomorph then this it, and as weird as the design is, this is what a Xenomorph looks like in some capacity. We can't say that is a Xenomorph and that David made them and then backtrack on that statement by saying it's not totally the Xenomorph.