Honest question, but what do you mean by artistic integrity? Are you talking about the techniques, the message, or both?
If you're working with an editor because you're both employed by the same company, then there's going to be a house style and a house worldview. You're not free to do whatever you want, but then again, you knew that when you signed up for the paycheck.
If the editor works for you, because you hired them, then you have the final word on everything. The editor can only make suggestions. And really, they wouldn't be doing their job if they didn't align themselves with your artistic vision.
I feel that an artist never really stops improving. There's always another technique to master, always another story to tell. You'll never stop learning until the day you die. The problem is that artists do die. Each of us has only so much time on this earth. So why not reach for every advantage? Why not get put yourself ahead of the competition by getting a mentor?
When I think of the purely-self-taught, I think of Srinivasa Ramanujan.
. . . an Indian mathematician who lived during the British Rule in India. Though he had almost no formal training in pure mathematics, he made substantial contributions to mathematical analysis, number theory, infinite series, and continued fractions, including solutions to mathematical problems considered to be unsolvable. Ramanujan initially developed his own mathematical research in isolation; it was quickly recognized by Indian mathematicians.
It's the "no formal training" and "developed . . . in isolation" that gets to me. What might he have achieved if he hadn't spent so much time reinventing the wheel? What mathematical discoveries and scientific advancements did the world miss out on?
A mentor can be a great help when it comes to technique. At the least, they can give one a thorough grounding in the basics (which many self-taught artists lack and which marks them). This doesn't mean that mentors lock their students in a certain way of doing things. Picasso was classically-trained and no one can say that he wasn't wildly experimental. E.C. Segar drew Popeye in order to annoy his anatomy professor. So you can't say that students aren't free to disagree with their teachers.
If anything, formal training helps you be more creative. "Learn the rules like a pro, so you can break them like an artist." as Picasso is supposed to have said.
A mentor can also be a great help when it comes to the message -- to the wisdom embodied in the work. Here's someone who's had the kind of career you want to have. He's had the kind of life you want to have. He's dealt with many of the same problems and had many of the same conversations. As far as one person can help another person find wisdom, a mentor can help you. In fact, this is probably their real purpose. Not only do they pass down the skills, they also pass down the philosophy of the art.
I'm not saying you can't improve on your own -- you certainly can. And I'm not saying you should feel obligated to take on a mentor or an editor. That's a personal choice. It is entirely yours to make.
But no man stands alone.
