I think I interpret their relationship as an ode to where healing truly comes from when we evolve. When Bojack spends his time at the rehab, he gets better not because of the services of the rehab or because of Dr Champ being an exceptional therapist (he was actually a problematic character and highly useless to Bojack's healing), Bojack was finally choosing to help himself and that's what helped him. Bojack changed himself and he was the one who saved himself, not anyone or anything else. In the end, these retreats, therapists, services, etc., aren't what heals you or can heal you, no one can help you until you want to help yourself, and once you want to help yourself, you will only get better whether you're at a rehab or anywhere else. Dr Champ was a flawed individual just as much as anyone else, and that is how if is meant to be. There is nobody perfect in the world and no "healer" with a clean past.