I'm glad to hear you got this figure out and thanks for sharing all these tips! I'll link the one with the screenshots the the FAQ as well.
If you save a route in MyDrive it's indeed converted to a track which only includes the start and end points. Route syncing works by design as you describe by choosing Send route to device after planning it.
There's currently no "auto-sync" as you describe but syncing routes and destinations is done through the quick menu. My Places are synced automatically when you save a new My Place either in MyDrive or your device/app.