I don’t speak French either but I like the etymological sense that Superior school means Post-Secondary/College better than the English version. It seems like a logical and efficient way to get the meaning across.
Not at all! There are many "Ecole Normale" which are just schools for teachers. The "Superieure" refers to the fact that you have to pass a hard exam to get in. And once there you can do research or become a teacher in a preparatory school (which prepares you to do the ENS's exams, in a pyramidal way)
That's probably what's happening, but I think I will keep the funny version in my head canon.