Honestly, think this is quite close to the nub of the matter. I can honestly say that in 15 years of mtb I've never thought that a great workout was part of it. Even when I was reasonably fit, it just wasn't a consideration. Am decidedly unfit now, nothing to do with the ebike though. But I can see that from the other end of the spectrum, it is cheating if the purity of exercise is muddled. Mind, there was a time when a dirt roadie face planting over a pebble would have raised a chuckle

Grown out of that now, more the merrier out in the countryside is my view.