I sense you are recoiling a bit from the notion of someone else raising your baby. This instinct is common to all writers, and is precisely why they need good editors.
A good editor is indeed a collaborator. If the writer is the artist with the vision, then the editor is the artist who helps him achieve that vision. From this perspective, the answer to the question, "what is appropriate for the editor to suggest?" is, "whatever will help the writer realize his vision."
Editors can certainly over-step, and when an editor tries to seize creative control from the writer, he has gone too far. But for the writer, who's primary effort has been to create, it is always difficult to throw away or change part of what he has created. So when an editor is trying to help a writer, often it feels to the writer like the editor is sabotaging him.
I recently edited a novel where a sexual assault was introduced to "heighten the stakes." The real goal of the novel was to depict the tragic death of a heroic young man. However, the shallow treatment of the assault, which had been perpetrated against the hero's love interest, pulled the reader completely out of his story. Indeed, the hero's own lack of reaction to the event (which the writer hadn't thought through) made him cease to seem like much of a hero, and as a consequence, his untimely death much less of a tragedy.
I had to convince the writer to either cut the episode (which was unnecessary to the story) or to give it it's due, lengthen the novel, and change it's focus late in the story. He had thought he was almost done with the novel. It was painful for me to send him back to the drawing board, and for him. But it would have been much more painful for us both to have had such a poorly executed passage in his published book.
Hope this helps.