David,
I don't think that your MS Answer Tech was giving you the full picture. It's not quite true that the Xbox Support site is responsible for all things Groove. A long time ago, when we had the Xbox Music app, that forum was where support was driven from, but since Groove came about, that is no longer the case.
The Groove team (in particular, Ellen Kilbourne) does visit this forum, in addition to the Xbox forum. It's true that issues take a long time to get addressed (if ever), but that is the case for both forums.
I get the feeling that the Groove team is focused on the Windows 10 Mobile app at the moment, and the Windows 10 app is languishing. It may be the plan of the team to roll out the Mobile app to the desktop as well (assuming it's a Universal Windows App), and so no work is being done to fix long-standing issues in the Windows 10 app.