The point of the article isn't to judge the value of the whole medical system, but rather to make a career choice. That means the relevant question is the value of the marginal doctor, not to try and get a representation of what patients see. We should expect that the marginal doctor is much less useful than the average doctor (i.e., the total benefit of the system divided by the number of doctors), and that furthermore ones expected impact of becoming a doctor is worth even less than the marginal doctor because if you don't go into medicine then someone else only slightly less skilled than you will take your place.