I agree with your overall sentiment, but I personally find googles fuel savings optimistic and/or flat out misleading. "Hey, you could turn off your usual route here and get there in a similar time.... Or you could stay on your usual route and save 2% on gas" seems to be a very frequent occurrence for me.

I also don't think that needs AI. The pathfinding algorithm just needs to apply different weights to the choices based on things like changes in elevation, number of stop signs, total distance, etc. Navigation systems from yester-year could do this well before the prevalence of AI. That said, AI can be used to develop and/or tune these algorithms instead of having a dedicated team of humans focused on this specific area.