Alien was not a big budget blockbuster.
James Cameron is the one who created the big budget crutch to the series by creating Aliens. But, this was not the fault of the creators of Alien. The money grubbing unintelligent producers of Alien decided to make it into a big budget franchise.
While typically I would say that big budget doesn't matter, in the case of Prometheus and Covenant, the big budget reputation of the franchise was definitely a crutch because it set up certain expectations from the audience. These expectations would not exist if Aliens and the films after that did not exist. I personally don't consider those films to be cannon, they diverge entirely from the themes of Alien. The themes of Alien don't return until Prometheus and Covenant.
Prometheus and Covenant and Alien are by design really difficult to understand, because the themes are not very politically correct or easy for humans to bear. The themes have to be hidden. They require some audience knowledge about nihilist philosophy. The biggest clue is "The Perfect Organism" lecture by Ash in Alien.
I have seen Upgrade. IMO it's not on the same level as I AM MOTHER and Alien/Covenant/Prometheus. I haven't seen Rememory ARQ and Infinity Chamber.