I can honestly say from experience that writing a novel is easiest the first time. It's mainly just laying out ideas- somewhat organized- on paper. It's most painful the second time. When faced with the mind-twisting pain of editing and rewriting, editors and beta readers are some heavy duty aspirin.
Before you start saying that no one has the right to mess with your writing, just let me give my sermon. Editors and betas provide that much needed "outside voice" that provides an opinion of your writing other than what you think of it. They suggest what may need to be changed, adjusted, or just plain deleted.
No protesting, I'm not done yet.
They also spot grammatical errors and if you hate having to worry about grammar as much as I do, this is a blessing. No one's grammar is perfect and no one knows how to spell every single word in the English language. When an author reads their own writing again, if they don't read carefully they can easily miss misspelled words since their brains know what it is supposed to be and will read it as that.
And then there's the all important "eye-opener" factor. What we may see as perfection can be far from it. Before you start prepping the army for retaliation, think about what they say. The best editor is the one that will not tell you what you want to hear, but what you need to hear. This is the reason I'm so thankful for Mary, who upon reading the first chapter of my novel told me that while I had a good hook to keep readers for the next chapter, the start of the chapter was boring and made my character seem boring too. I looked back over my first chapter and rewrote most of it. I'm glad I did. The next time Mary read it she said that it was much better and she found my character much more interesting. Your characters are always interesting, it's just how you write them. Remember, criticism is a ladder disguised as an anchor.
So remember, show some love to your editors and beta readers. They don't want to see you fail, that's why they can be harsh, but being harsh means they care. The next time someone tells you something needs improvement, don't just ignore it. Their suggestion may be the factor that gets you published.