Can't speak about ProPilot, but I've noticed the Adaptive Cruise Control on my Honda Clarity responds much more clumsily than I do. Rather than gradually slow down as the traffic ahead slows, it seems to wait until the magic car length has been breached then it slows much harder, over slows a bit, and then takes a long time to recover once traffic speed resumes. And since it over slowed, it then has to do more acceleration to get back up to speed or reach the magic car length it is looking for. I haven't measured the efficiency aspect as you have done, but I can see how the different driving behavior would adversely impact efficiency. The Clarity PHEV lacks a battery % display, only presenting bars, so rather difficult to measure unless I bother to use the phone to get a more accurate reading. I guess they figure that since it can run on gas that level of granularity in battery level info wasn't that important.
This stuff is still bleeding edge tech and has a good bit of development room.
'13 Leaf SL
'18 Honda Clarity Touring PHEV