I don't really see it as a petty sense of not wanting anyone else's stuff to be as successful as his, but rather, just him exerting the power that he was handed over the decade or so from Prometheus' production to now, where he basically had carte blanche to steer the ship for these ten or so years. He seemed cool with Blomkamp's film co-existing alongside his own for a while and then just all of a sudden wasn't - presumably because Blomkamp's movie would have conflicted with something he had in the cards for Covenant or its followup. If the studio is going to give him that power, it'd be silly to think he isn't going to use it.
Now, under Disney, he has less power but he's still the same old Ridley. Back around the time Ron Howard was brought on to salvage Solo's production, Ridley Scott was asked if he would ever be interested in making a Star Wars movie, to which he responded "No, no. I'm too dangerous for that." Alien isn't as big a brand as Star Wars and likely isn't quite as micromanaged by Disney/20th Century Studios as Star Wars is by Disney/Lucasfilm, but I'd imagine that to some degree the sentiment does still apply - Ridley is, to a certain extent, too dangers from the studios' perspectives to allow him to go completely unchecked with the material, as he has no real concern or regard for the limitations that franchise filmmaking tends to impose, the limitations that the studios are usually all about maintaining within their brands.
His disregard for those limitations, his desire to take an established property like Alien and and shake it up and use it to explore whatever is currently interesting him that can be analyzed through that property's unique lens, is one of the things that makes him and his works so exceptionally interesting in the current climate of blockbuster franchise filmmaking, in my opinion, and the main reason that I find so much to like about Prometheus despite the film's plethora of issues.
