The big banks don't write code in K4 though, managers generally encourage people not to write code in it due to the difficulty of finding developers who are fluent in it.

They all use q and q is very wordy and highly readable if you speak english. It's mostly just developer defined functions which are compositions of the keywords of which there are not many: https://code.kx.com/q/ref/#keywords

Most of the code you would see in a kdb+ system in an investment bank won't look like any of the links you've provided.