Thats a big sudden jump to take with no hints of alien outer space features in previous Xmen movies.
Dark phoenix chapter was fine being chosen to be the main story for this movie, just needed to slowly but firmly introduce alien concepts. I think they should have basically followed Man Of Steels story structure. First 15 minutes opening sequence is set on a ShiAr home planet as the phoenix force is destroying it and the ShiAr with Lilanadra are fighting against it - similar to Krypton, displaying wacky creatures, costumes and alien architecturel design. Phoenix force eats a star, kills lot of ShiAr and runs away towards earth looking for a new host, with Lilandra following. Then basically the story picks up where Kinberg starts, with the space mission. Rest of the story happens on earth, fast forward to the end where the ShiAr arrive to destroy the phoenix as revenge, and fight the Xmen in a big city like Metropolis in MoS.