*sticking my nose in*
The thing is...discussions like this ("Who has control") always seem to me to be viewing the editor/author relationship as an adversarial one. It's not, or at least it shouldn't be. An editor suggests changes, and I can assure you as someone who's now been through the editing process over a dozen times with several different editors/publishers, that 9.9 times out of ten the editor's suggestion will make sense and seem like a good idea. Honest. The editor just wants to help you make the book stronger; they're not out to hurt you or anything.
That one-tenth of a time? Well, that's different. Usually you can just say "Eh, actually, I kind of like that the way it is," or "That relates to something that will happen later" or whatever, and the issue will stop there. I have in the past disagreed with an editor's suggestion and the response I got was "Okay, no problem." I have once in the past disagreed with something the editor felt strongly about, and it took a bit of discussion for us to reach a compromise. But it was NEVER adversarial; it was never angry, it was never an argument, it just required a bit of thinking. I'm certainly happy with the finished product; I don't look back at that book and think how much better it was/would have been if only I'd been allowed to do it MY way or anything; ultimately it was a very small point.
I've never felt that I wasn't "in control." I have no problem telling my editor(s) I don't want to make a particular change for this reason or that; I have no problem STETting copyediting suggestions I feel change my voice. And no one has ever had a problem with me over that.
Editors and authors work TOGETHER to make a book the best it can be. The editing process is generally fun, at least for me and a lot of my friends. Sure, there are moments when you want to roll your eyes or grumble, but for the most part it's genuinely fun, and I enjoy it, and afaik editors do, too.
An editorial letter isn't an edict. It's you and the editor working together to make the book stronger. I have in the past resolved an editorial suggestion not by making the suggested change, but by changing something else, thus making it unnecessary. You the author have complete freedom to do that.
It just kind of bugs me when I see the idea that someone wins or loses in editing. To me the editor/author relationship--much like the agent/author relationship--is a partnership between two people who have experience in different areas. Don't think of it as someone having "control." Think of it as someone helping you make your book better.
Just my 2p.