>Almost all "programming" problems have been solved. Today's software is laughably inefficient not because we need better implementations of data structures, but because putting all those existing pieces together properly is a neglected discipline.

YES!

But You learn that writing low level code, not high level.

Writing Text editor, or even a compiler, you don't spend much time on algorithm optimization. You spend it on designing good abstractions. You are given basic tools, and have to come up with good architecture on your own. And because you are forced to use more levels then with pre-made libraries (that create the structure for you), you will see your mistakes much faster.