Hi, FYI I've been putting bikes on all sorts of cars for years, but not electric ones, which are clearly heavier.
My sixth penny worth is:
The ones which just fasten to the ball, can be dodgy, as they rely on a clamp to the ball, they do however strap back to the vehicle, whether window or spare wheel, which can be very secure. To your advantage I'd rather strap back to a spare wheel.
The better ones have a plate which sits between the two bar plate and the ball fitting, but this does not apply to swan neck set ups. As this way the chassis is taking much of the weight, they are also strapped back to the window or spare wheel. They are usually a pole and arms which slides into the towbar fitting, and can be removed when not in use. Dead strong and very cheap, lots on ebay, new and second hand.
Third issue as you've mentioned is how far the cycle rack can span out to avoid any interference with the spare wheel, this will be your deciding factor. And I think the set up immediately above gives you more strength. You can cut and weld the cheaper ones to either straddle either side of the wheel or span out further.
So food for thought, but which ever way you go, be 100% certain the setup up is solid, attached solidly, and has plenty belt and braces(straps) in place. Also protect any bars with the rubber sleeves, (the bike frame normally sits on them)and I always carry old foam or yoga mats to put between bikes to stop damage but allows with tightening everything against eachother, this way without scratching etc. As electric bikes are fecking expensive, especially when you see them in the rear view mirror cartwheeling down the road into following traffic.
good luck and enjoy the bikes
Ali