Often, Blair's quick-wittedness makes it possible for Jim to make the arrest, close the case. This is not the behavior of a child, a dependent, or a lesser being. This is the behavior of a capable, responsible adult. Maybe it's hard for the authors to write about Blair as an adult who's working with courage and resourcefulness in a job he never envisioned because the authors don't know anyone like that to use as an emotional role model. If that's so, I'd suggest that they look around a little more.
People change careers all the time.
People face difficulties in their lives and surmount them with courage and humor, without reverting to childhood. An injured Jim is still considered to be Jim, strong and intelligent and capable and just temporarily sidelined. He's still considered a man with a problem, not a child with attention deficit. When I look at the show itself, what I see is two men who fight their way through difficulties to friendship, who start by using each other for their own purposes and along the way discover that they are both equals and friends. They become partners, complementary, creating a relationship that's as complicated and interesting as any in fiction or Real Life.