One thing not mentioned yet is the time discrepancies between OSM, GM, HERE and TomTom. When switching a route amongst these maps, waypoints and mileage are effectively unchanged, but the duration can vary significantly, sometimes by hours. I know my daily riding limits, and plan routes by both distance and duration. In my experience GM seemed to have the most accurate timing, so I used that for planning trips and created HERE copies for my Garmin GPS.
So I will greatly miss not having GM route calculation capabilities, but I understand and wholeheartedly support your decision not to renew this feature.