It's a balancing act. You're absolutely right in the observation that the hero is the client, but when a coach tells their own story the reader builds trust. They think, "this person had the same struggle as me and understands what the process is like, therefore I will trust the to relate to my problem and the find a solution." A client also likes knowing that others have trusted you prior to them.

But the website should always be focused on what the client needs because and if they need to hear your story and credentials, that's great. But do have content that asks them about their pain points and the results they're looking for.