Honestly though I don't think things would have been any better without Scott, Blomkamps big budget Hollywood stuff has been crapola IMHO and you can see whats happened to Predator and Terminator. The Scott prequels I would put above all those films, terrible scripts but they do actually have a skilled director involved in them, actually why their more disapointing as you can see they could have amounted to more.
That is the bar for Hollywood running these franchises in recent years though, not much reason to believe Scott has been holding back something better IMHO.
You are correct that post-District-9-Blomkamp has been awful. Elysium was mediocre at best and Chappie was absolutely terrible. And the Oats Studios shorts that he has been doing the last few years don't inspire much confidence in me. They have the exact same problems...they look pretty good, and fail everywhere else.
So there isn't a LOT of reason to have great confidence in Blomkamp's Alien 2.5, but I still would trade in Ridley's prequels to see that instead.
1. It's not Blomkamp's original property. He ran out of original ideas and characters after one movie. But in this case, he's taking someone else's world and characters and continuing, and he seemed to have the one thing so few sequel makers seem to have these days...some respect for the world and characters.
2. It would be a little easier to just toss it in the trash with the rest of the dumb sequels if it sucked ass. It would not have been made by the original director from the series, and it also probably wouldn't try to dismantle the lore and world like these prequels. We could probably just Alien: Resurrection the whole thing and hand wave it away.
All of that said, I don't know if Blomkamp is the guy to write the screenplay for Alien 2.5. And I'm almost sure he's not the guy to light a fire under Michael Biehn and bring back the Reese / Hicks / Coffey / Ringo version that owned the screen.
But I think Blomkamp would make a great #2 guy handling the visual effects to a director who knows all of the intricacies of story and acting. Kind of like Jan de Bont back in the day. Blomkamp doesn't seem to know shit about acting, he just kind of lucked out and got a real self-starter in Copley who doesn't need much direction. Meanwhile he gets bad work out of Jodie Foster, middling work out of Sigourney Weaver and Dev Patel, atrocious work out of singers...