to use your scenerio....what happens when denise sales with ma and pa because he is doing his bottom.....the rest of the phrf fleet gets boxed into oblivian because you are trying to rate crew and not boat.....not saying it can't be morphed into some type of system like that but it wouldn't be PHRF...
same reason golf style stuff won't work....you are rating one guy on his individual performance.....what do you do when one week you have the A list crew fresh from key west race week and the next you have the island of misfit sailors that don't know which end is the bow.....