Things are different when you have a publisher. You're not on your own any more, you're part of a team, and other members of the team have more skills than you do when it comes to certain aspects of producing a book.
In fact, you have only one skill: writing. A most important skill! There are maybe 90,000 words in your book, those words are what got you here in the first place, and if the words don't work then you and your team are doomed. But being able to write does not make you an expert on sales, or marketing or production, or...graphic design.
The basic rule of thumb is, the writer owns the words. The publisher owns everything else, in particular, the cover and the title. I've read of some authors feeling excluded by that, but not me.
Just because we own different bits of the job doesn't mean we shouldn't listen to each other. Editor Kathleen writes me a lovely editorial letter with suggestions for making the book better; always suggestions and always with the rider that what I do is up to me, because I own this bit. I could choose to ignore everything she says, but since I'm not insane I listen to an expert and behold, the book gets better (in particular a character list which I would never have written if Kathleen hadn't encouraged me, but which I slaved over and now am very proud of).
The reverse is happening too. I'm having a magical experience with Kathleen and Minotaur on the cover. They own this bit, but they've been fantastic about asking my opinion. There's a clause in the contract which says they should consult, but Kathleen's gone so far above and beyond consultation that I very much feel it's a joint effort.
Right at the start Kathleen asked if I had a vision in mind for the cover. She sent me some samples (actually entire books!) to prompt ideas. I scanned a cover of a book I had and sent it to her, saying, "Something like this?" Kathleen could very reasonably have said it wouldn't work (in her usual polite way), but she didn't. Instead she ran with my thought and suggested a variation. We talked it back and forth. More variations. She talked it over with others inside Minotaur, particularly her boss, Keith. The vision simplified, but it's still the vision.
So it's our combined concept that she's taking to the intriguingly named Jacket Meeting in the future. (I wonder how many people have used the Straitjacket joke I instantly thought of when I first heard the name of that meeting?) At which point the sales and marketing people could replace our lovingly wrought vision with something completely different, because they have to sell this thing and their opinion matters a lot. But that's not the point; the point is it's a team effort.