I think the reason that Fuji has a fourth colour layer is mainly because they've always done exagerated colour in their consumer films. Consequently Im guessing they needed another layer to tame in any skin tone side effects. The other reasons are that they dont have a film phobia and have kept pumping money into film research.
Remember, I was shooting the film with a EI of 320, which saturates the colours even more. I just dont think Kodak has enough degrees of freedom in their film with 3 layers to provide "ultra colour" and natural skin tones..