The invitation - *minor spoilers inside*

My partner has just commented - the "invitation" map points to the planet that we are supposed to find... yet when we get there we find that is isn't the home planet but the planet that is a "weapons facility" like in the desert - away from their home planet, where we find the ship that is ready to fly to Earth to spread the virus?. Why would they want us to find them on the planet where they are preparing to come and get us? And why would we be visited thorughout history by the Engineers and be told to go there? Were they breeding us so they could use us against other alien species? Maybe their race was being used by the Xeno race and they were breeding us to be used instead of them?