I've worked with overbearing editors who change everything, whether it needs it not. In fact, I once found a magazine story I'd written and didn't recognize it! The copy editor had added about six inches of copy to the story at the beginning, something I haven't seen before or since. Was it better? Maybe. It was certainly more dramatic. Should he have done it? No.
The editor for the magazine apologized and told me that particular copy editor often re-wrote stories. "I guess it makes him feel more important," the editor said about the copy editor. At the time, I wasn't happy.
A few years ago, I worked with a terrific editor who re-wrote my leads and endings to his taste. He'd ask if I liked them, and I'd say they were OK. They were OK, but they weren't better than what I'd written. But the checks didn't bounce, so I didn't complain. Besides, I admired that editor then, and I still do.
Another editor used to change my football stories. I'd write that the QB flipped the ball over a defender to a running back, and the back dodged two tacklers and raced 80 yards for a touchdown. He didn't drill the pass; he flipped it over someone. The editor asked if he passed the ball. I said yes, and he changed it to the QB passed the ball to the back, who ran 80 yards. Instead of giving the reader a vision of what happened, he changed it.
I can't complain, though. This guy has fixed my factual errors and a few times added information that made a story better. Generally, he's made me look good (just not when anyone was flipping a pass).
I worked with another editor who seemed to think that boring leads were a good thing. He'd re-write my lead, then send the story for my approval. I'd punch it up a bit and send it back. He'd accept the new lead almost every time. Finally, I figured out what he would accept and went ahead and started writing those leads. He wasn't a natural editor, so I helped make it easier for him.
Another editor would look for any excuse to cut copy. She'd ask dozens of questions. After each, she'd say, "We don't need that." If a person wasn't quoted in the story, she'd cut him out. Of course, she might cut him out even if he was quoted.
Me? A good writer has nothing to fear from me. I'll change passive voice to active voice, add a nice turn of phrase and generally try to let his/her voice shine through. A bad writer? Well, I'll re-write it if necessary. My aim is to help the reader, as well as the writer. Generally, a good writer can't even tell that I've been there.
Of course, most editors, even the bad ones, do good things, too (although I'm not sure about that guy who re-wrote my magazine story). On a good day, even a bad editor can be a big help.