The US is not comparable to W Europe or the EU on this topic, since neither of those are political units responsible for a healthcare system. However, that brings us to your next point
>scale is also a matter of division...
This is a great point. However, for whatever reason, we have never seen a successful single-payer system in a US state. Even very blue, wealthy states have not achieved this.
>scaling a system to support 5x...
Again, the data does not support this. I don't have a reason why, just observing that it's not supported by real life.
Hm, with regards to the difficulty of scaling these systems specifically and really the whole topic at hand more generally I don't know that there is sufficient domain specific data to justify a viewpoint either way. I mean how many examples of scaling a national healthcare system (public, private, or otherwise) to support 300+ million people do we have? Literally three, right? The US, China, and India. Each of which has such significantly different circumstances that comparing them is less apples to oranges than it is apples to giraffes to glaciers. That being the case I feel like it's only reasonable to draw upon non-domain specific data wherein so far as I'm aware and in my experience we see a pattern of scaling existing systems being simpler than originating new ones.
You're right that we only have a handful of countries operating at this scale (~150M+ populations) so it's not exactly "data" in the common tech-sense of that word.
I want to get back to my original point: it's not "astoundingly clear" that the US should have a single-payer system (not your words, I know). My own thoughts are that this is mostly a scale problem as well as an inability to properly assess the performance of other systems (e.g. I would call both Canada and UK healthcare broken, but others see those as successful).
I agree that the US system seems broken from both an "Outcomes vs Cost" and a "Cost over Time" perspective. I just disagree that nationalizing healthcare, either through a single-payer system or the current Obamacare system is the answer.
>scale is also a matter of division...
This is a great point. However, for whatever reason, we have never seen a successful single-payer system in a US state. Even very blue, wealthy states have not achieved this.
>scaling a system to support 5x...
Again, the data does not support this. I don't have a reason why, just observing that it's not supported by real life.