Actually, that's just but one of the many variables. Skin type, type and density of whiskers, prep time and procedure, water temperature, shaving cream/soap brand, lather consistency, shaving style, etc. all play significant parts in how a blade works for a particular person.
I agree, but, if I am testing a new blade, I do not choose a new shaving soap, shorten or lengthen my prep time, etc. yadda yadda, and change all the variables you mentioned. I want oranges to oranges. I suspect that most of us do as well. The variable is the blade. Still some guys love feathers, some hate em. I am skeptical that one brand of shaving soap will work with feathers and another will not. All things are possible but some are not as likely as others. That said, I still agree with previous member that the most likely variable is the relationship of the razor to the blade, as we all use a multitude of razors. I am pleased using derbys with most of my razors, but not all of my razors. Nothing is different but the razor.