Just my humble opinion, but it seems Medicare for all would only exacerbate the actual problem of medical costs being too high due to government subsidization. I'll take my down votes and go now...
I will say that I recently had to deal with the medical system for a family member, and he was on decent private insurance. We actually would have received better care at a lower cost if he was on Medicare instead. N=1, of course.
I'm pretty sure that Medicare has been shown to be a more effective negotiator than the private insurers and generally operates more efficiently, but I may be misremembering.
Disclaimer that I don't support medicare for all myself, I'd much prefer a model closer to the NHS, with caveats (federal funding, county administration, state oversight).