Nice experiments, thank you for sharing!
I think, the main difference is the length of the profile near the hub and the area covered by blades near the hub. This could prevent a flow back of water near the hub. Also the thickness distribution is different, the commercial design looks more rugged and will deform less. Three blades instead of two also gives less load for the prop and also mechanical deformation.
Here you can see an example of commercial propeller 180mm cut down to 140mm diameter. There is a slight camber which becomes more distinct the more i cut away. (I turn this in the reverse direction to get less hard strokes when the tool hits the prop, so the gear is not worn too much. Therefore the tool is also mounted in reverse direction).