Have both, and here to tell you a gear driven hub drive and mid are both heavy when pedaling with no power.....
Direct drive hubs are like dragging an anchor in back of you with no power.
That said, I don't plan on using either with no power! People can if they want of course, but I think once you use it, you'll find having the power on more often than not will be most normal.
Before her first e-bike, the wife was concerned about the exercise aspect as well. Stating that very CLEARLY, over and over. That was a big concern for her going into this. She soon found, as I did, that's a complete non event. With a half decent bike, you can use as much or as little power as you want. Getting exercise will NOT be a challenge....