European city bikes are most definitely not built to go 25 mph. A Dutch step through bike with a backpedal brake at 25mph would be very sketchy.

You'll add approx 20-30 pounds with the battery and a hub motor to the frame and that can make stopping more difficult, it's not the same as a heavier rider.

Not sure what you mean. The range of weights on any given adult bike beyond, say, extra small, are much wider than 20-30 lbs. It's exactly the same as a heavier rider as far as stopping distance.

The handling of the bike with weight added on the frame (especially if it is high) is quite different under a hard stop than just adding a heavier rider with the same weight.

You can shift towards the back of the bike with your body for instance.

> especially if it is high

Like the body of a larger person or a person wearing a backpack?

I mean where you mount the battery pack on the bike. On a rear rack above the tire is probably the easiest but its not great for stopping or handling, especially if its more than ten pounds.

On the down tube is better. Carrying the batteries in a back pack can be done. I did that for a few months.

Since the battery and the motor are usually low on the bike, it's actually a little better than a heavier rider.