Unless you have knowledge to the contrary, I'd dispute this. Most physicians, and specialists in hospitals in at least the Pacific North West are NOT hospital employees.
This is how you can get into ridiculous situations where your hospital is "in network", but your provider is not (because of course, you get a choice on the physician you are assigned at a hospital, especially in ED...).
First, it "penalizes" doctors/hospitals that take on the most severe cases. There is no objective metric for "we saved X people who would have died at an average facility." Do you want a metric that would encourage a doctor/hospital to deny an aggressive procedure for fear of taking a hit in its mortality metrics?
Secondly, it ignores ongoing quality of life. A cardiac surgery can have a later death that does not count in its mortality rate, even if it was due to a complication caused by, or significantly contributed to, by inferior medicine.