Apple Sierra deleted GarageBand still taking up 1.76G of space!
OK so.... after posting this, on a whim I decided restarting my laptop to see if that purged anything extra, even though it was still showing the 1.76G being used. I didn't think it would make any difference, but I suddenly remembered that was always worth a try when dealing with things like this.

Gonna answer my own question by saying, once you've actually followed the above linked-thread, restart your computer!

Storage Management now shows Zero KB of space being used for "Music Creation". GarageBand is no longer the space hog it was. Huzzah!