Come on Erik, What do you expect Mitsubishi and Grafalloy to say? When you say that a co-engineered shaft is virtually the same, I agree, but only in paint scheme. In order to change the torque or kick point of a shaft, you have to have a completely new "recipe" and make up to create that shaft. More than likely, a variation of materials used for said blueprint to achieve the desired "tweak" as you put it. That in itself puts the "co-engineered" shaft into a name of its own and totally separate of the "after-market" shaft. Is a blue board co-engineered by titleist a blue board... sure, in name only.
Purely speculative on your part, but what do you think a company that doesn't "co-engineer" shafts for club manufacturers, would say on this topic? It's going to be completely contrary to what you stated. I know, because I have spoken to a couple. So, you have two sides with two conflicting statements. Which one is true? Probably neither, the truth lies somewhere in the middle I would assume.
Put an after market Kha'li on a launch monitor against a "co-engineered" Kha'li. Pay attention to the dispersion and spin rates... it tells a story in itself.