There is gross waste at every layer. The AMA artificially keeps doctors' earnings higher than they would be in a system that could respond to demand.

How are they keeping earnings high?

Restricting supplies of doctors.

How is that supply restricted? Medical schools are pretty much full, but many schools are going to great lengths to expand available spaces. Med school enrollments are up about 30% since the early 00's. It's true that at some point in the 90's the AMA was predicting an over-supply of doctors, but they quickly realized that wasn't the case and reversed course, as evidenced by their own (successful) efforts to help schools increase enrollment (https://www.aamc.org/system/files/reports/1/enrollmentreport...)

Additionally, restricting the functions of nurses, physicians assistants etc in the process.

A lot of things that doctors do (because people want doctors and doctors want doctors to be in demand) could be done by nurses with special training.