Right, that would be a good argument IF we were talking about a bunch of random people whose rank is completely unknown, and in fact this sort of heuristic is the usual, common sense one that leads to the situation we're describing (and that can be exploited).

The KEY information here is that they're at the same rank. That means the slob has had to overcome people using the heuristic you've just described in order to reach the same rank, probably through being an objectively better surgeon.