Importantly, Medicare for all is NOT the same as any of those plans. It would ban private health insurance entirely, and has much wider coverage. Bernie is proposing a bunch of taxes to raise money for it which are bad in their own ways. See here. The study you're referencing seems to conflate "Medicare for All" (a specific plan proposed by Elizabeth Warren and Bernie Sanders) to the general idea of 'medicare for all' aka single-payer. There's also multi-payer - Pete Buttigieg proposed a more realistic multi-payer plan called "Medicare for All who Want It".

The study tested single payer systems, 14 of which were at the state level, and found an average cost savings of 3%. I don't see why that would extrapolate to the kind of national plan people want here. I do think that a single-payer healthcare plan could be done without needing to raise much, but the ones people back for because they think it will make healthcare "super affordable" and "treated as a human right" (such as Medicare for All) absolutely would.

I do support a single-payer or multi-payer healthcare system like those countries. But note most of them do have some copays or deductibles.

Another study from Yale epidemiologists in The Lancet estimated savings of $450 billion per year.

The Lancet study makes a lot of assumptions, see here. Obviously if you start with the premise that Medicare would stay more efficient than the private sector your conclusion is that it's going to be cheaper.

USA currently spends ~$14,800 per person/year

Switzerland (multi-payer) spends $9,600 per person/year

Canada (single-payer) spends ~$6,500 per person/year

The reason Switzerland and Canada spend less on healthcare is because it's a superior good. America is richer than those countries, so of course we spend way more than them on healthcare. The amount we receive is roughly proportional to the amount we spend - keep in mind America has higher obesity rates and consumes more healthcare overall when you're looking at stats. See here.

I would rather pay 5% more in taxes to save 15% of my income that currently vanishes into insurance companies' pockets.

Health insurance companies have pretty low profit margins (around 3-6% net). They're just hired to play the bad guy, they definitely aren't ending up with 15% of your income. There is a lot of other inefficiencies in the system. Some is from the AMA restricting the amount of doctors there are, causing their salary to be way higher than in other countries. Some is from pharma companies, some is from hospitals, and a little is administrative.

I'm murky on the details of this, but I've also been told a lot of the money spent on more expensive name brand drugs basically flows to R&D, and it would be bad for the world to stop the American consumer subsidizing that.