No one should've marketed this as an Alien film or prequel. The premise is interesting enough on its own, and it only shared some themes with the original for the most part. It has larger ambition, a different focus and message that leaves it more as its own thing.
The fact that it is connected to Alien could have just been easily made as a twist, and it would have probably been received differently. Most Alien fans who saw this back when it came out seems as if they went full-on CinemaSins and its really unfortunate.