I don't think I need to do that at all. Demonstrating equivalence seems entirely sufficient.

EDIT: Wait, I totally misread your comment the first time round, and yes, from the position you're approaching it, the argument isn't complete. In the context of the original spoon/spade argument, I think I'd need to demonstrate that the person with the pre-2002 photography degree can't accomplish equivalent feats to a person with a contemporary photography degree, adjusting for experience.

In this case, it seems that the contemporary photography graduate has the advantage of not having to learn a large quantity of material that is no longer necessary with the advent of better tools. This points to a possible difference between badass spoon-diggers and obsolete spoon-diggers: the badass spoon-digger develops general skills, whereas the obsolete spoon-digger develops obsolescent skills.

EDIT EDIT: Some explanation on this particular example -- this is a complaint I've heard a couple of times from people with such degrees, that they spent a lot of time learning how to achieve effects which are trivial under contemporary methods. From their perspective, this was time wasted.