It really isn't Garmin's fault that you chose to use a zumo 450 which doesn't support Track navigation. You also aren't using the same maps that Google is using so you have no "road" to Route on hence the need to Direct Route from Marker (waypoint) to Marker. Did you try using the latest CNNA in BaseCamp instead of the Topo map you show you are using? The route you have mapped between Mt. Baldy road and Lytle Creek is available on the latest CNNA (Barrett-Stoddard to Big Tree Cucamonga).
Blame can be placed on Garmin for not fixing the KML/KMZ Import translator. When this is fixed you will be able to save your Google Map route to your My Places and then save that path to KML format on your computer. When BaseCamp gets the KML Import working you would simply Import the KML path as a TRACK into BaseCamp. There you can edit the track so that it will work on your zumo 450 as a Direct Route or convert it to a Route is you're using CNNA.
Today, since the KML Import isn't working, I use GPSBabel to convert the KML on my Mac to a GPX file. Then I import and do whatever I need to do in BaseCamp.
Hope that reduces your workflow a bit.