Orlando,
In regards to purely moving water, needle wheels are inefficient compared to props. Same reason why boats and airplanes don't use needle wheel designs. Its obvious why when looking at the designs. Needle wheels are designed to slice through the water. Traditional props are designed to displace water.
Higher RPMs = motor working harder. If a needle wheel pump is pulling higher rpms for an equivalent amount of water movement, then that's less efficient.
Using an overpowered pump to maintain water movement while preserving the needle wheel effects is one way of addressing inefficiency.
Charlie