Yep, depends on the power of your motor and the power used by your legs.

I use about 250-300 watts each (motor and legs), but that is rather unusual. The real question is, are you pedaling as hard as you do when you are not on an ebike? If so, you will get the same amount of exercise, if not you will get less. Its up to you.

I could pedal a good 300 watts on a 1000+ watt ebike. It wouldn't make much of a difference to the bike, but I would be getting a workout.