You are arguing as if what is available today, right now, at this very moment, for today’s retail prices, and today’s specifications will remain static. With any technology, it will improve exponentially for the better, while prices plummet. 20 years from now the 20 mph bikes will weigh half of what they do right now, cost equivalent to what $400 is now, and have a 100+ hour run time before you have to set them in the sun for a two hour recharge
Remember cell phones? Plasma TVs, 4K TVs, laptops, tablets? Remember when the idea of electric cars was a joke? Ever heard of Tesla?
The rule is a mistake.
20 years from now, for half the price of a new bow, you will be able to take a motorized vehicle that goes 20 mph and doesn’t need charged all week on trails that last week were closed to all motorized access.
If it does need charged, you can probably park it in the sun while you hunt.