When it comes to your editor, absolutely. This one is a no brainer as far as I am concern. Editors are expensive. I have seen authors let this part of their book slide. After all a writing group or beta readers can do the trick, right? We know this is wrong. You can’t get away without an editor to help you get your book in the best shape it can be in. But you can fire your editor if they don’t do your book justice. There are so many editors out there, good quality ones, so don’t feel bad in giving your editor the shaft.
Illustrators fall into the same category for the same reason. There are many illustrators who, like editors, rang in price and also range in talent. If you feel your book cover is not properly representing the words behind it, why stay with this person? Granted, it is tough coming up with a cover that you are happy with but sticking to what they give you shouldn’t be an option.
Lastly, can you and should you fire your publisher? I can’t say yes any more clearly then yes. Writers get so giddy when a publisher wants one of their works. Something I truly get. It is exciting, amazing, wonderful and oh my gosh A PUBLISHER WANTS ONE OF MY WORKS! But it doesn’t mean you have to take their offer or stick with them to the very end. It is not a marriage that can or will live happily ever after. Yes there will be pitfalls, what relationship doesn’t? But also like a marriage when it is not good for you it is not good for you and a parting might be what you need.
Bottom line, this is your book You are the one who wrote it and spend gosh awful amount of time and effort creating it. Doesn’t it deserve the very best you can give it?