They're not assumptions. I'm talking about what is likely vs, what is contrived. If you accept Alien 3 and Resurrection as canon, then it is a FACT that there are no further recorded encounters with the aliens between the events of Alien 3 and Resurrection. The exception to that being if there is some sort of convoluted inner-cabal at Wal-mart / W-Y.
However, if you don't count those films as canon, and you have a blank canvas in front of you, then it is more likely that you would encounter the aliens again after 30 + years, than 2 years after. Again, this takes into account that the derelict is destroyed, which has to be a fact if Alien: resurrection is considered canon. The odds of running into the aliens again completely independently of the derelict within 2 years are slim. Just consider how long it is taking us to find any indication of extra-terrestrial life right now.
Your concern is that we would have a scenario where Ripley once again accidentally encounters the aliens, which would put her in some sort of super-hero territory. How could one person have so much bad luck? Your concern is valid, and I don't think anybody wants that. The fact that we actually already have a super-hero Ripley as per A:R notwithstanding.
I don't think retcon proponents want to have a desire for a gloomy or overly cheerful film. They want something that is likely and realistic.
If you consider Ripley's encounter with the aliens in the Aliens film, it is not coincidental. She doesn't run into them randomly in space. She has moral motivations that don't allow her to ignore the plight of families that are exposed to the aliens on LV-426. She has a legitimate motivation to encounter the aliens again. The motivations in Alien 3 are unlikely, and in fact contrived. The odds that she would be so stupid as to allow the aliens to remain on the Sulaco are slim to none.
So, ignoring ALien 3, if she finds out 30 years down the road that the aliens have been discovered again, randomly, by some other people, her response to intervene, would be a likely one, and it would be fully consistent with her character, without taking her into super-hero territory.
It's not about people wanting a perfect happy family thing as you are always saying. Nor is it about wanting the Alien universe to be unrealistically gloomy, where everyone has to be killed off as per trope. People just want the alien stories to be grounded in realism and likelihood. Blomkamp's film offers that possibility. Will it deliver? Who knows? But it is the best chance right now to fix the core story in the series.