The beginning to Prometheus explained

Re-watching the extended part of Prometheus at the beginning when the Engineer sacrificed himself, still didn't give me the answers that I want. In the alien covenant trailer, we see the covenant ship flying over a lake with a waterfall (the same one at the start of Prometheus) ... wait, but he created humans by doing that... so earth is paradise??? WHAT. If you watch a guy explain the movie (with the best theories and evidence there is) it'll give you a reason how and why he did that. So, the theory is, they created us so the Xenomorph could have a host (thats what the black goo does, it can create a species and a host for the species... SUPERGOO) at the beginning of Prometheus, he was getting the planet ready for the creation of humans and xenomorphs... pretty cool right!!!! What do you guys think?!