Being about anything effectively makes it about nothing. The IP becomes meaningless -- when you pick up an Alien title are you getting a story about Aliens, or are you getting another generic scifi?
General public sees Alien, wants Aliens, which is how IPs work.
Yes that's an issue I have with Prometheus as a single film. (Four Seasons of Black Mirror beg to differ in terms of the general concept though of the subject matter changing substantially episode by episode.)
Besides I never said it can be about just anything, just that Prometheus' indecisiveness opened the door a lot wider, for all that room in the genre itself.
As for the public wanting Aliens... and yet Prometheus still struck gold financially anyway.
It's enough to have the "DNA of the Alien" in it, if you can not find an appropriate place for it, we will all have to get used to this being the status quo going forward anyway:
Because the Aliens will not be appearing episode by episode, so you will hopefully have great episodes that by necessity will not feature the Alien once at all, and like a recent horror on Netflix that might even be the best part.
And if it follows the structure of Fargo as I expect it will to a degree as an Anthology as originally reported years ago, and it is successful enough to continue on, you will inevitably get whole seasons without an Alien to be seen.