I’m not sure about that, as I’ve seen conflicting information. Medicare has existed for around 60 years, and not only have patients been more satisfied with their care on average than people with private insurance, the costs have also lower than private insurance overall. Couple those factors with metrics from the most recent study I was able to find on the cost of single payer, and the picture seems a bit muddier than you’re presenting it.
www.ncbi.nlm.nih.gov/pmc/articles/PMC8170543/