The US has proved it can do horizontal scaling, as the majority of adults gets a college degree.

The horizontal capacity is ineffectively used by having many degree mills and low-value degrees, but if we re-tooled the knowledge sets we could raise the bar.

I actually think of degree mills as being vertically scaled. Online courses, a lot of course work graded by computers, large classrooms, etc.

As for the quality, I think small classrooms with good teachers probably produces a better outcome than large classrooms with great teachers.