I thought it was documented that a British editor did the first rough cut?
In any case, the Oscars Marcia Lucas, Richard Chew, and Paul Hirsch received for editing Star Wars speaks for itself.
The way I know the story is that a British editor (not sure how he became involved) did a cut without Lucas really watching (I think he was busy), Lucas sees it and hates it, scraps it and starts over with new picks, who each take a chunk of the movie under his supervision and in collaboration with him.
And as I noted above, De Palma vouches for Lucas’ editing skills.