That's not actually entirely true. There are at least three scenes that go over the ALIEN DNA.
The scientists at Anchorpoint do a human-alien culture to see how the alien DNA reacts. What they see scares them they terminate the experiment. Takes the ALIEN DNA seconds to basically destroy the human tissue culture. The corporate suits insist that the experiments follow through, and what develops in the container is actually not far from the spore pods in Alien Covenant. Something goes wrong with the system and it causes a couple of the tubes to overheat/over pressure and crack. A small egg-like spore has developed, and when it comes close to two of the characters it opens and releases a "small cloud that disappears." They're both infected with this new strain.
The commies basically admire how well it "lends itself to be manipulated" and that it seems to be almost "manufactured." They're impressed that it has a "universal compatibility." IE, whatever you give it, it will use. Basically, it's the perfect organism, a survivor, unclouded by conscience, remorse, or delusions of morality.
So they do explain it. The Alien DNA will simply change and snap back violently depending on how it's cultivated. It makes more sense than the random nature of the black goo and spores.
Literally nothing about what goes on in the Gibson drafts, particularly draft 2, "contradicts" the first three films, because the way the Alien species is introduced and explored is different.
Also, after rereading it, i'm really curious to see what they do with the Stoiko. It's brief description in the script makes me think of Crimson Tide in space... Cold War space battle wagon.