I think you are right about the multi blade props. If you look at the airfoil on the props in your pic and compare to MAS or APC you can see how you lose efficiency. This means more power to get the same thrust. Sorry I don't have the airfoil curves to show you. However if you get the air foil to match the better prop you can improve your multi blade results but won't match the same amount of thrust / power input, at least in the model category. The real herk used them due to high power turbines and limited space for a 2 blade prop due to engine spacing. (engine spacing,, sound familiar in relation to prop size).

You must consider on a model the time for blade 2 to enter the same airspace that blade 1 just left is very small due to the diameter and circular speeds. On the full size herk ( at least the E model as I remember ) THe 4 blade prop turns 1021 rpm,, much slower than a model engine and when blade 1 of the full size space is occupied by blade 2 a far greater time has elapsed and the blade has moved through the air stream much furthere. This allows for cleaner air and improves efficiency.

Hope this helps you with your work. Merry Christmas.. Jim