Interesting posts and opinions.
I suppose I'm in the group that agrees that emtb can help you get fit, but (BUT), it all comes down to what are you willing to suffer.
From my short experience with Emtbs compared with bikes, ebb can make you lazy, or faster.
Why lazy?
You just let the bike push you uphill... and you just go along with it. It will be faster than any bike, and you'll complete any ride faster than any bike.
Why faster and not lazy?
Yes, I've stated that being lazy on ebb will be faster than most on bikes... but, if you start pushing the pedals on the climbs, reaching the speed limiter, even using Turbo, you will be FITTER than a tradicional bike (from now on, just bikes).
1- you will ride more. More time=more fit
2- you won't arrive from ride feeling dead! You will be ok for next day, and the next, and the next. This is the same as when you are fit and slim (younger??) on a bike! You will want more! (See point 1)
3- it will be FUN to ride. You can pratice DH runs, you can exploit areas that you would probably never do on a bike. This will lead to point 1.
4- you will try to climb stupid steep climbs, that not only will end in enjoyment and fun, but you'll be making series (or sets)... something that any biker hates!
5- since you descend more, your upper core will be more used, you'll feel the need to have more core exercises out of the ebike, and it will be easier to do so, because you'll notice much improvement immediatly (because you descend more on an EEB)
6- since it's fun and can climb fast, you can have a blast in 30/45min, and due to this, you'll make time to ride the emtb whenever possible!
Doing all this, will lead to:
a) lose fat, making you slimer and looking better (I lost 3kg in about 2 weeks)
b) lower your heart rate at rest, and feel much better
Depending on your fitness level:
1) in a couple of weeks if you have some fit
2) in a couple of months if you're not!
Bikes (Normal bikes) can lead to proscrination since it's hard work!
Steep difficult climbs don't leave good memories (in my case, even when I was fit 99% and weight 10kg less).
If you're not fit, it's easy to let go...
With bikes, everything will be much, much worse, if you're group ride is fast!
Eeb, is the opposite.
As you get some fit, you will challenge yourself.
If the eeb & fitness kicks in, you'll start doing loops non-stop, having a blast in the uphills, downhills, flat and squezing a ride almost everyday.
You will not only have a blast, but serious milages and accumulated height on your rides and year!
And the thing is... getting fitter on a eeb is easier, and will become much more satisfying any bike ride!
In my opinion, EEBs don't replace BIKEs, they complement (A bit like MX/Enduro/Triao motorbikes)