My wife has a class I ebike and it's the difference of riding or not riding/barely riding. With her non-ebike, she was basically toast just getting a few hundred yards away from the house. Everything is about 4% grade. So, she could ride for a few minutes, be total gassed, and she was done.
With the ebike, she can do 20+ mile rides lasting well over an hour, is pedaling unless coasting downhill. She takes on steeper hills that she still can't make it up (9%+) giving it her all. But she's getting a little farther up those. So, is getting fitter.
She's clearly getting much more exercise with the ebike than she would otherwise. And just as obvious, less than she would get, IF, she could do those same 20-mile rides without an ebike. But she can't, and is unlikely to every ride without the ebike.
Obviously if you do the same ride at the same pace, you're going to get less of a workout with an ebike. But certainly in some situations the ebike provides a wider range of workout possibilities and this could very well lead to better workouts in some cases.
Another perspective, if all that matter was how hard it was to pedal, then I guess we would all get a better workout riding a bike with under-inflated tires, and dry, hard to turn wheel bearings. Let's throw in some brake drag while we're at it. But I think most of us prefer some higher level of performance than a rusty old bike would give us. Why is that? We all know, it's more fun to ride smoothly and easily than to be grinding along.