It's probably not an issue when it comes to riding dynamics, if you hit a pothole though even at 45mph it's going to be hard on the spokes in the wheel and the wheel bearing.
I would observe that although a hub motor is certainly likely to be heavier than any alternate drive scheme, it does eliminate the mass of the sprocket, its mounting, and 1/2 the mass of the chain from the unsprung rear axle. For a drive shaft bike, the rear gearing and 1/2 the weight of the drive shaft would be eliminated. I think it's probably that belt drives win the least rear axle mass contest.
As AzCal Rtd pointed out, using a hub motor reduces overall weight of the vehicle by eliminating duplication of a hub structure in the separate motor.
From my perspective, the biggest negative of the hub motor is the fact that the motor can't benefit from torque multiplication in the drive train. Torque is limited by diameter, magnet strength and current limits. There are available hub motors with internal planetary gear systems that allow the motor's rotor to spin much faster than the wheel, and I suspect that the motors on these E-motos are constructed in that way. When they develop multiple ratio, internally geared hub motors, I think we'll see more manufacturers move in the direction of hub motors.