I understand your point. But let's also look at the view of a commissioner.
If I commissioned this image, and gave that reference, it's because I want that exact pose.
Now I understand where you're coming from. If an artist took the time to figure out this exact pose, took time to understand how the anatomy is going to work, then you feel it unfair others can build off that by simply drawing different characters in their own style.
But, as a commissioner, that's what I would want. If I have no idea who that artist was:
-How would I then commission them for the same image with different characters?
-What if the original artist created the image exactl like the screenshot to a porn clip?
-Would it be wrong of me to commission another artist for it?
-What is the difference between me using another image as an exact reference, over a porn clip image? Is it not essentially the same?