Well, I don't know anything about Gymnasium, but it doesn't sound very different from K-12 compulsory education in California. Except the many languages and computer science-- children learn to program in Germany? That's amazing.
I don't think the average high school-educated American is a drooling retard (contrary to popular belief...), but the onerous General Education requirements of bachelor's degrees provide additional breadth of knowledge.
Learning multiple languages is a necessity in Europe, it's handled similarly in the surrounding countries.
> and computer science-- children learn to program in Germany?
The basic courses don't get further than Excel macros, but in the extended courses it's fairly solid (data structures, algorithms, multithreading even back before multi core CPUs were a thing, …).
> but the onerous General Education requirements of bachelor's degrees provide additional breadth of knowledge.
That seems to be the difference, then. Our bachelor degrees are already limited to domain-specific knowledge; you're supposed to do several degrees if you want to further broaden your horizon (arguably not entirely unreasonable if it's free).
Computer science education seems to vary a lot between high schools. It basically depends on how good your teacher is. (Each state also has an official curriculum.)
I don't think the average high school-educated American is a drooling retard (contrary to popular belief...), but the onerous General Education requirements of bachelor's degrees provide additional breadth of knowledge.