In addition to training new doctors, we should also just loosen restrictions for doctors to enter the US and use their medical expertise.
Kaiser also recently opened their own medical school: https://en.wikipedia.org/wiki/Kaiser_Permanente_Bernard_J._T...
So they're now using a mixed strategy of both out-sourcing and in-sourcing medical training to address high costs.
Not as much as they could though - there are still federal caps on the number of fellowship seats available as well as pretty strong restrictions for physicians coming from overseas (although if I recall correctly, California has less stringent restrictions than most)
We discuss insurance as a big part of the cost problem, but regulatory capture on the supply end is another huge (and unnecessary) factor.
A crisis like this would be the perfect opportunity to fix some of these supply side issues. Lobbying is less effective when voters are paying attention and the government is in crisis-response mode.
This process continues in intern year and residency, during which time they gradually build competency and trust.
Much of medicine in the US is delivered by nurses, who have a training regime even more similar to what you suggest.
Things have changed rapidly in medical education. At least some places.
Why not make it like Engineering?
You do your 4 year undergrad and at your first job, no one trusts you. Your supervisor/senior engineer checks Everything you do. You are reserved for paperwork and unskilled manual labor which is also checked. After a few years (4) you get some Freedom, but still checked by your seniors. Anything important, even when you are a senior engineer goes through your Managers and directors.
I don't see why this system wouldn't work in medical. We build airbags and bridges. Both safety critical.
I would even say having 1 physician is more dangerous than having a team of Engineers with less Schooling.