I work with lots of Brits and their education is not superior-- just more specialized. Compared to the schedule listed above, for example, over the first two years of my local public school, the students would have another science, probably a physical one, like Chemistry. So, over thos 2 years, they would have: English Language and Literature for both years, Math for both years (here, the average student takes Geometry and Algebra II at the beginning of high school but, throughout the country, Algebra I and Geometry are the more typical sequence), one foreign language for two years (at my local school, the typical student is either doing level 2-3 or 3-4 in the first two years of high school), Biology, Chemistry, U.S. History, U.S. Government, at least one year of art, one year of physical education/ health and two more years of *something* which could be a second foreign language, computer courses, additional science, etc. The school system here operates on 7 periods a day, so students would have 14 years of classes by then and have 2-3 hour finals in all the academic classes at the end of each year. By graduation from high school, they would have taken 28 credits.
At my public high school, back in the 80s, we took 8 classes at a time. By the time I graduated, I had studied three foreign languages, as had my sister. One of my kids also graduated ps with credits in 3 foreign languages (one through AP level, one through IB level and the other was Latin, of which he had a reading level). It's not that it can't be done, it's that, in public high schools, more than one foreign language is optional and few Americans are interested in doing that. They're more likely to take computer classes, for example. So schools often schedule different foreign languages at the same time because it causes a conflict for few students. This is less of a problem in large schools or school districts with a lot of foreign languages. There is a lot more interest in Europe in learning multiple foreign languages.
By the way, I've asked my British coworkers who have children in our public school system to compare it with theirs and none has said ours is easier than what they studied. The only problem some of them have had is transferring their child in at the high school level because I don't think the studies align well. Most of them end up having their kids finish high school in whatever system they started.