Quite a lot of Germans learn quite a lot. German schools expect quite a lot from students that do actually want to go to better schools. But yes, it is possible to slack through it all if you want to slack.
Bavaria, Saxony, Baden-Württemberg? Preferrably Gymnasium? Preferrably a state school, not a city school? Hell, you have good chances!
Any other Land? Something on a lower tier? Nah, easy going. There are schools in Germany which are famous for breeding 16-year-olds who can barely read.
Disclaimer: Writer is German, Württemberger, visited a state gymnasium
Hey, you are the genius who knew it all before learning and got highest possible grades with no effort. Congrats.
Overwhelming majority of people is not like that, they do not get highest grades, they do not get into gymnasium without effort, don't pass tests without effort.
My point is that the actual content of school material was very low, especially compared to university.
Of course I did actually learn the material of the tests, but the actual learning outcome of my schooling is far worse then it could have been, given the 12 years invested.