(Again, I don't necessarily agree with devolving as far as possible, but isn't it philosophically hard to argue against?)
Philosophically, I would say that a country or nation can only be successful if some common things are equal for everyone. Letting individual groups opt out and in of stuff as they want, just destroys the overall community. And you end up with "haves" picking the cherries while the "have-nots" are left with crap. And nothing in between.
Why is decision making at a lower level wrong? And why is decision making at a higher level not better? Why did you pick 'state' level and go with that?
Ok but I can say 'maybe country B is richer, then country B might not want to fund schools in country A, leaving those desolate'.
Why's that not the same?
Sure, some teachers go on to set policies ay the ministry. Those are actively teaching anymore. Of course there is so much more nuance to it, but in a nutshell that's it.
You have an elected government setting policies. You have public servants acting on those. Democratic and surely somewhat technocratic. But it works.