I've not watched the video, but I will and reserve the right to change my text if appropriate.
When I got fit for my irons the numbers were telling the fitter I needed a lighter stiff shaft, but I wasn't getting very good results, the fitter had the idea to put a heavier regular shaft in instead and it was chalk and cheese.
Now I know as amateurs our swings are not consistent enough to fine tune to the Nth degree the same way the Pros do, but we can tell when something is not working and in the instance I mention about my fitting, a lesson or several could've got me to use the stiff shaft, but the fitting was about getting a shaft that worked for me at that particular moment, not one the fitter thought was best and that I could be lessoned into.
So while someone with a consistent swing can make the most of any shaft making the appropriate changes to adapt to a different shaft, a shaft for us mere mortals is what works for us with the swing we have.
**On You Tube there is a Mizuno video with Nick Faldo going though the Mizuno swing DNA tool and fitting, it's a little long for some to sit through, but Faldo does give some nice insights into the fitting process old and new.