If you think that the debate over healthcare has anything to do with the substantive merits of one system over another, you're viewing it through the wrong lens. It is purely a power struggle between a class of potentates who have become obscenely wealthy from selling insurance, and the vast majority of the public in whose interest universal healthcare is.
Medicare for All being a success in one state would change little by just adding more evidence to the existing mountain because, again, it is not a struggle between differing points of view, but between monied interests and the masses. The colossal propaganda apparatus wielded by corporate interests would continue to wage relentless war against any expansion of such programs.