Yes, I think it needs to be said again. The mural depicts a deacon, not a xenomorph. It's an important distinction. The xenomorph, while similar to a deacon, is quite different aesthetically. The long tail, the inner jaw, the bio-mechanical tubing, the human skull, etc. The mural doesn't contradict anything. We can only speculate at this point about the nature of a full grown deacon, but it's possible that a deacon is more...let's say, intellectual than a xenomorph. While highly improbable, maybe deacons are the antithesis of the xenomorph. Either way, the mural indicates that the deacon is an ancient entity, and David being the creator of the xenomorph doesn't mean he's the creator of the ancient catalyst. He's just manipulating it. If anything, this should make people salivate for more deacon information.