John N Great points John.
I agree with you on the data privacy, but also realize, what I consider, significant benefits from the data - case-in-point is the heat map.
As you note, though - new routes don't show up on the heat map as the data has not been there to have been aggregated for the heat map.
That is a big nudge for RWGPS, actually. I have found RWGPS fairly good (I realize there has been a "glitch" with the "surfaces" feature that launched here in recent times, but its easily worked around). I did some test rides on my Ohio to Erie Route - my access routes to the "trail". Those started before I started using RWGPS. Once I worked with RWGPS, on my southern route, I knocked out several miles of busy road riding. Some of the trails were asphalt walking paths that were only 2-3ft wide (no joke) that I felt a bit stupid riding down with a loaded touring rig. But - I wasn't on a busy road. The point is - the detail of the trails is pretty well up-to-date, at least here (other areas I can't vouch for much - I can see some areas being behind) and it can help tremendously.
Of course, out in the boonies where there are no local trails you are reliant on roads. Thats where keeping an eye on the satellite views and elevation profiles are key - as well as the heat map.