My knowledge of muscular dystrophy is limited, but I do know that muscle weakness is one of the symptoms. emtbs are surprisingly heavy. Heavy enough that I switched from putting the bike into the back of the car to loading it on to a bike rack on a tow bar (saves my back). The extra weight makes manhandling the bike around the garage, cleaning it, and so forth a bit more of a challenge. Then there is stuff like when you are actually riding the bike as that extra weight requires a bit more effort to move the bike around. Have you actually ridden one yet?
Like you, I did loads of research before test riding any bikes for real. That was useful, but nothing can replace the actual ride. Bikes I thought would be good turned out to be less favoured once I'd ridden them on a proper mtb surface. A bike I was only liking because of how it looked but had spec concerns turned out to be the winner for me.
How far are you likely to ride? if your rides will not be so far, then maybe you could go for one of the bikes with a smaller battery. Or maybe one with an integrated battery. These tend to weigh less, because the frame does not have to be strengthened to cope with a great big hole in it. Smaller and integrated makes them even lighter. Carbon fibre frame, lighter still. Higher spec tend to be lighter also.
But maybe I'm looking at this the wrong way around. If your problem is not muscling the bike around, but one of endurance. In which case you are likely to be in the higher boost modes sooner and for longer. In which case you may prefer to go with the larger battery options. Most emtbs have a 500Whr battery, some have less than 400, some have 600, one has 250. The Focus Jam2 and Sam2 have a 378Whr integrated battery with the option to add another 378Whr battery on to the downtube, making almost 760Whr.
This is an interesting topic, please keep us informed of your progress and eventual decision. Best wishes for your future riding!