Ok, lets assume that the benefits of economies of scale don't apply here and take that it doesn't work for systems with hundreds of millions of people as a premise.
We know it works for systems of up to ~50m people because those are the larger EU countries. In that case I submit that it would also work at state level in the US. I feel that you can't even make a good argument that the reason it can't work at state level is because of the federal government because we're also a de facto federation within the EU and it works for the most part.
edit: I'm likely missing or wildly underestimating something here but I just can't shake the impression that what prevents the US from having all the nice things we get are cultural and historical issues, not economical ones.
The biggest obstacle that prevents humans from doing anything is their own culture. Resources can be found if there is a will.
Here is no different. Many people hate the very concept of public education, let alone throwing more money at it. And when people do agree that we should do it, they inevitably disagree on the hows and the whats.
The issue with scale isn't logistical or so... metric based. It is as simple (and insurmountable) as getting such a diverse population to agree at all.
We know it works for systems of up to ~50m people because those are the larger EU countries. In that case I submit that it would also work at state level in the US. I feel that you can't even make a good argument that the reason it can't work at state level is because of the federal government because we're also a de facto federation within the EU and it works for the most part.
edit: I'm likely missing or wildly underestimating something here but I just can't shake the impression that what prevents the US from having all the nice things we get are cultural and historical issues, not economical ones.