> Dermatologists are hit or miss.

That's even relative to the condition you have. The right match of doctor to condition gives you the right treatment. But the same doctor facing a different condition might be clueless. From that angle, the whole situation looks less weird.

The quality of a doctor then could be measured in how many conditions they are good at, maybe weighted by likelihood of occurrence, as well as how self aware they are about whether they have a clue or not.

A corrollary is that a single data point does not tell you much. "Go to this dermatologist, they are great" is only good advice if you have the same condition as the recommender as their sample size is likely very small.