Not all editing is alike. Not all writing is alike either. I get calls all of the time for different kinds of writing skills. Clients often don't understand the difference between ghostwriting, editing and proofing.
Ghostwriting is writing for someone else on their behalf and then making it look like they wrote it. Many people have a story to tell, but they aren't professional writers. They are either looking to professionally publish their stories or they just want something for friends and family. A ghostwriter though does most if not all of the writing.
Editing is more global. The editor is looking at the overall content and the grammar and punctuation. A great editor will also do what we call book coaching. In looking at the entire story, the editor provides feedback and guidance to improve either a nonfiction or fiction book or just content for websites and marketing materials.
Proofing is drill-down and specific. The proofreader AKA copy editor is looking at every detail to ensure grammar, syntax, punctuation and style are correct. A great editor isn't always a fantastic proofreader and an excellent proofreader is not always a good editor.
In the editing and writing departments it's rare to have one person with all skill sets. It may not make sense but I've worked with great editors who are okay writers, and I've worked with good writers who are not good editors. You can't necessarily lump it together. We use at least two editors on manuscripts. I'm what you would call the editor-in-chief and editor (book coach) and then I worked with another editor who is more of a proofreader. You always want more than one set of eyes on your work. One person just can't do it all. Even if that person is really good at who he or she does, it's very hard to be a jack-of-all-editors. Getting a book nearly perfect is a real feat when you're working with some 50,000 words. So value the editorial profession. It's takes more skill than you learned in high school English.