It doesn’t seem like residency is the main culprit. Canada and the U.S. require a 4 year BA + 4 years of medical school, where most European countries combine that into a 6-year medicine program.
https://www.theatlantic.com/ideas/ar...doctor/622065/
It stands to reason that if the time and cost of schooling is a major barrier to practicing medicine, then reducing both by 25 per cent would increase the supply of physicians. Residency spots would have to be increased too.