You're citing Matt Breunig's figures about how much more efficient Medicare would be than private insurance. But the truth is, mechanically, the opposite. Medicare's efficiency is a statistical illusion. Administrative overhead is a simple ratio of fees paid to services rendered. The more services you render, the better your admin costs look. And Medicare's look good indeed, because virtually everyone in America over the age of 65 is covered by Medicare --- that's the point of the system, to do single payer at the point where costs suddenly ramp up. If you let people enroll in Medicare at age 25, they would incur
lower service costs, while paying
the same in fees. If you do the math, Medicare for a 25 year old looks a lot like private insurance for a 25 year old.
Meanwhile: all insurance costs, in the whole economy, across all of national health expenses, total less than 10% of costs overall. Providers drive all the costs in our system, not insurers. But Breunig is fixated on his preferred solution, so he's not telling you that. But the numbers are right there if you want to see them; just search [National Health Expenditures by Type of Expenditure and Program: Calendar Year 2022].
I honestly don't care if you want Medicare vs. private insurance. I don't love my insurer. But if you zero out the total cost of insurance, public and private, you barely make a dent in our health costs. There is no way around it; the numbers are stark.
Personally, I think the balance we've struck in our payment system --- private markets until age 65, at which point the state steps in --- is pretty smart. Our system is fucked, of course, but that's because health provider chains have been ripping people off for decades.