Only treats one or two patients a week.
Needs 3-5 other fulltime doctors to help him.
Always misdiagnoses patients multiple times.
Often only reaches the right diagnosis through luck or coincidence.
It's a prestige thing. He is well known to be among the best diagnosticians in the world and the cases he works while often rocky are too complicated for regular doctors and usually end with the formerly doomed patient surviving. While he causes trouble for the hospital, they can also boast about having him to attract affluent patients, not necessarily to be treated by him but because if the regular doctors on staff can't figure out what is wrong with you, he'll take the case. He is an advertisable safety net.