If competence is, as the article suggests, normally distributed, then there's no natural level at which to draw the cutoff line. But anyway, iirc, studies show no correlation between outcomes and class rank (nor selectiveness of medical school), at least for surgeons.
A. Mister.
IOW, this joke/insight is only valuable if the standard for passing is set too low.
If it's set correctly, then everyone who passed has shown they are prepared to be a competent doctor.