I know it would be political suicide, but I do believe that we could still have a very good medical system if the level of education we demand of doctors was reserved for surgeons and leadership and the front-line work of GP-style treatment was 100% left to people who were qualified by a normal nurse-style process of undergrad + apprenticeship + test.
That's kind of how it works outside of North America. Students go into medical school right out of high school, and medical school is about 6 years - maybe including residency. They graduate with a degree that allows them to practice general and family medicine. If they want to become specialists, they keep studying and more residency.
North America seems to be alone in requiring a 4 year degree before letting a student anywhere near a medical school.
Also "rest of the world" the medical professionals do not get into massive debt and hence do not need massive compensation upon graduation to offset. One issue of getting more supply of doctor would, I believe, be the resistance from the current system since more supply means lower prices...
Additionally since a lot of our healthcare is managed by Private Equity or other forms of investors that are looking for a profit, I suspect with cheaper staff they will just keep prices the same and increase their profits.