Isn't "better" a subjective thing? What's good for one person is bad for the next.
Honestly, I think the NEEDS are different between the Japanese and American markets. That need drives the product... whatever it may be.
I think it's pretty safe to say that on average, the American golfer has a higher swing speed. That being true... the golfer might need a different bend profile and different CG placement in the head to get the desired results. Now if a person with a slower swing speed tried this product, of course they would not like it... it doesn't fit their NEED. What they would need is a shaft that spins the ball more and a head that gets the ball up quick.
What technology does each one have that the other doesn't? What different materials are used? Heck, they are all pretty much made in the same place, right? Are you going to tell me that they use different material? Maybe they won't care about assembling this product vs. that?
Just trying to see how you can measure "better". What "fits" is the best.