Mid-drives vs Hub-drives
Higher end bikes will have mid drives systems because of their versatility and efficiency. However, on the flats, a hub motor drive in generally adequate and less expensive.
Things to consider:
A - Center of gravity
B - Hub drives Increased wheel weight and impacts wheel rebound
C - Hub drives utilize more amps when climbing
D - Mid drives are more difficult to install
To further clarify the situation with 'unsprung' weight it should be noted that relative to the ground the wheel is sprung by the tire. The tire is fundamentally a compressed-air-filled balloon with very little inherent damping. The more mass that is sprung only by this 'balloon' the less influence the rest of the bike's structure (suspended or otherwise) will have on damping any bouncing it wants to do when excited by bumps.