My Norco 6.1 e has a rear drive and 9 speeds. It will go up any hill loaded with a 200 pound guy and gear so long as you are moving at the start. I can go up a ditch bank so long as I am moving a bit to start and pedal a bit. Some friends kids were using it and doing jumps off the side road and getting air borne. The one kid or young man weighed well over 200 pounds. I guess he was not a kid... 20 years old.
As far as rocks or logs or muck it will not work well unless the muck is shallow. If you hit a rock or log it will and has knocked me off my bike. Your center of gravity is high so that can be expected. But I can go through knee high grass ag fields trails with no problem.
I suppose it is not any different than a game cart in the wrong terrian.
One disadvantage of gears on an e bike - they can plug up with grass and mud over time or quickly if conditions are bad.
The rear drive motor is not a problem for torque, gears or anything else. I just bought a second e bike for my wife. It is an elby with the same bionix engine and panasonic battery. It has a 3 year warranty and is built by Magna... a very large international auto parts manufacturer based in Ontario. Yes it is Canadian made and not made in China.
I paid 2999$ cnd dollars for her bike and mine. Or $2400 US dollars each. A mid range priced e bike that is not junk and well built.
Well built, good warranty. I have had my bike for two years with no problems.
Both bikes come with hydraulic disk brakes and regenerative battery capabilities, It will charge the battery if you put it on negative assist or when going down a hill or when you brake. It has 4 levels of assist... 30%, 65, 100, 300%. I think those are the levels of assist. It also has a throttle so you do not have to peddle at all.
Her bike is not a fat bike but we intend to ride it on local bike trails. -- an old rail line.
I doubt many ebikes have the same warranty backed by a reliable company. You get what you pay for. I like my ebike. They do not make the Norco 6.1 E anymore but you can buy the same e bike kit from Bionix and put it on many bikes.