Trikester you have a funny point on the hot exhaust, because many riding pants are made from nylon that melts pretty easy. I believe all my riding pants have a melted spot. Good points on what we encounter when riding offroad. In many trails, I am probably going from 5 to 25 mph, so if 1 gear can handle that range pretty well, then I think I might be better off not having to shift gears.
I have encountered that sudden near vertical step when going up hill. It is decision time, can 2nd gear handle it, or do I need to drop it down into 1st. If I drop it into 1st, will I will lose too much speed and not be able to make it. Almost no time to make the decision on a surprise obstacle. I kept it in 2nd, got the rear tire over the step and then stalled. It was too steep and loose so I slid backwards even though both tires were not rolling. Once that rear tire went over the step I fell over fast and learned elbow pads do not have protection on the back of your arm, tricept area. I sort of take that lightly now, but at the time I was actually quite angry, and thought I might have really damaged my arm pretty bad. E-bike would have been better in this case.
Now how about this theory. Gears on an e-bike would still give a choice to the rider. Even though I would not need to shift when riding a trail between 5-25 mph with just 1 gear, would I like to ride a certain section of trail using a different ratio? It is like changing sprockets, but I don’t have to change them, I just click the gear selector and now have a different drive ratio. Perhaps any of the 6 gears would work in that trail, but they will all work differently. With gas bikes you can’t use all 6 gears for the same trail. 6th will just stall out and 1st is just too slow. So perhaps gears can be used somewhat differently with an e-bike. Not as a necessity to make the bike go like with gas bikes, but as a preference thing.