This statement may or may not be true depending on your operating point. By operating point I mean the Q ( flow rate ) and total static head and pipe losses. In centrifugal pump selection we started of by deciding what flow rate we want. From the static head and pipe loss head calculated we know the total head. With the known flow rate and total head we can determine what is the power required to drive the pump from the pump operating curves. If the pump at this operating point needs a 1/2 horse power motor well and good you have a maximum efficiency pump. However if the operating point requires a motor say slightly bigger than 1/2 hp. One would have to select a 3/4 horse power motor, in this situation the electrical efficiency would be lower.
For submersible pump the manufacturer is able to tailor made the motor size to suit the pump power requirement to limit wastage. As far as electrical efficiency is concerned the trick is to select a pump operates at optimum efficiency at a given flow rate and head. Centrifugal pump may or may not be more efficient than submersible pump, but one thing is certain, non submersible centrifugal is more reliable and certainly last longer.