So, I backed up my drive to an export then deleted the Legend folder. I actually had two folders…probably a result of switching between accounts a while back. This made no impact on my storage allocation (I waited 24 hours to check).
Finally I discovered that GDrive has a separate space for “hidden app files”. It’s accessible via Drive Settings –> Manage Apps. That area included an entry for Legend and while it didn’t tell me how big it was, it took a real long time to clear it out, and now 24h later, those 11GB of storage are freed up.
So my short-term problem is resolved.
This post stills stands as a feature request for more controls around GDrive backup, in particular how far back to keep those backups.
But I have to ask if you can explain how 11GB of files got ferreted away as “hidden app files” in my Drive and attributed to Legend. Bug? Edge case resulting from beta use and too much experimentation? I think it’s worth at least asking the question.