Well yeah - your manager should be coaching you, but to be your only coach? Naw. Listen, I'm sure your manage is a great, but can you honestly say they're objective? Of course not. They need you to perform well so they can look good and keep their job - they are inherently subjective in their coaching..
That's where I come in.
I'm objective. I want what is best for you and your highest self and I separate that from the business - even if they are the ones paying for your coaching.