It sounds like the assembly/script is told chronologically. First the prologue with Weyland, then about 12 minutes of David and Shaw, followed by the bombing scene. Scalia, as an editor, is concerned with not only pacing, but a structure that has a balanced shape. He thought it was taking too long to get to the main story. Let's face it: even with all of the Shaw scenes restored, she's still almost completely irrelevant to the story besides providing some of David's motivation. Scalia was looking for something to cut, and he and Scott disagreed about what those cuts should be.
We know Scott fought to keep the bombing scene, so his idea to speed up the beginning was to lose the even more irrelevant prologue scene. It's a nice scene, but it's also the most expendable one in the final cut. It sets up themes at were already set up in the prequel at great length. But it's a shorter scene and a less time-consuming way to open the film. Scalia's idea to speed up the movie was use a small part of Shaw's footage as a flashback and use the Weyland scene as a thematic prolongue. To Scalia, this was the most balanced way to structure the movie. In effect, he sacrified story and character in favor of pacing, structure, and theme. He goes on and on about theme and pacong and doesn't show much consideration for story.
That was regrettable. On essence, Scalia would rather that Covenant work better as a standalone movie and sacrificed connecting to and building on Prometheus. Prometheus already set up David. The prologue, while nicely shot and admirably spare, contributes nothing that a Prometheus fan didn't already know. Imho, Scalia was too concerned with the impersonal details of structure and pacing and disregarded something that rival studios have figured out: fans want the story to build over each new movie, connecting the emotional dots. He didn't pay enough attention to tracking e story from the perspective of the audience. He did what he liked, not what he should have done.
Sorry, Pietro, but your editing ruined another Ridley movie. He's a damn butcher. He needs to stop trying to fix stories in the editing room. He did the same to Prometheus, thinking that the structure needed fixing when it didn't. Having flawless pacing and a balanced structure is secondary to tracking the story in the way that allows the audience the deepest experience.
Scalia has hacked so many Shaw scenes from this series that I have to question whether he is an appropriate choice to edit them. Scott makes epics. A long buildup is the hallmark of the Alien series. The more I hear about Scalia, the less I approve of his values. Pacing should never harm story, yet time and again Scalia compromises the story and argues that it was the only way to get perfect pacing. No wonder he's more interested in David than Shaw. He sacrifices the heart and soul in pursuit of structural perfection.
There was another option: a 12min flashback. Scalia overrates the importance of pacing and is all too willing to butcher the narrative in order to do it.