> Babel cannot gather code from external files into a single place

Yes it can. org-babel-detangle copies edits you make in a tangled file back into the matching source blocks in the Org file. There's also `#+INCLUDE: "file.py" src python :lines "10-40"` and org-transclusion package - `#+transclude: [[file:foo.el::some-defun]] :src elisp` shows live content from an external file in the Org buffer.

Babel has no built-in way to import arbitrary existing files, but for the stuff that you make it make sense, it knows how to get its shit together back into one place.