Well I am not aware of any study on the hydrodynamic properties of BP/W vs. jacket BCD...but I can tell you that my BP/W has far less material and fits far more snugly to my body than any jacket style BCD I have worn. That is measurable.
Hose routing and danglies have nothing to do with it.
It might help if you quote the posts you are speaking too

herman:A couple of thin straps on a divers chest of a BP may look more streamlined but when you take into consideration the area of the divers chest covered in a wetsuit it is basically the same total area as the frontal area of a properly fitting jacket BC the difference becomes small. The real difference in streamlining between the 2 is in the rear of the BC and that is where the jacket style wins. From personal observation I do know (or maybe feel is more correct) that the bladder on a BP adds a huge amount of drag.