Humans aren't Xeno incubators

I would just like to discuss the feasibility of the hypothesis humans were created to simply breed Xeno's. I find it unlikely and here's why: 1. 4 Billion years is a long time to wait simply to develop a weapon, especially if your at war. 2. It's a particularly a long time when what you have is already an excellent weapon. And the black ooze is certainly easier to deploy than adult Xeno's. 3. The beauty of the Xeno is you don't need them in mass to do a lot of damage. 4. Why would it require the sacrifice of ones own people. Why not just mix DNA with the goop. Okay, so my opinion is in line with the sumarian post. I think it makes sense that there is a creator race responsible for the space jokeys/engineers and humans. The engineer at the beginning of the film was a sacrifice by the creators to create humans but also as punishment for the engineer rebellion. The engineers creat or re-engineer the Xeno's as a tool for revenge against the creators and the humans, which either backfired on them or is sabotaged. It also explains the weird smile and affection the engineer shows toward David, possibly because they are both creations. Of course it's complet speculation, please comment.