Long time Office user here, since Word 2.0, in fact.
I know what you mean. Event though I'm fully subscribed to Office 365, on a new document I hit Save, get Backstage, I ignore this (cos I prefer standard Save dialogs) and click "More options" (or Browse) to get the Office Save dialog, then I save it to a folder (that is in the OneDrive folder) in the conventional way.
I mean Backstage is OK but I just prefer a conventional dialog (I've literally learnt just now that clicking the up arrow takes me up a folder level - so this tells you how intuitive the Backstage is). Also this new dialog is OK but is it going to list all my folders in OneDrive? No?
Can't Microsoft just make Backstage, this new dialog or the Office Save dialog an option instead of layering 3 different Save "experiences"?