I don't disagree with you, in theory. What I'm saying is that there's more that goes into the "feel" of an action than just pivot length, the hammer movement, up and down weights, etc; the things we often talk about here that we can measure more easily. As Gene was saying, there are various frictions involved at different points of the system, for example. I think beyond just an initial up or down weight, there is a certain momentum the key will have based on how quickly you touch the key, etc. It's complicated, and an extremely good synthetic key folded design could address all of those aspects. More likely, they've addressed a couple that can easily be measured, such as pivot length and down weight, maybe even friction/resistance during key travel. But is that friction constant or does it change over the course of the keystrike and key return? There's only so much they can design for without the extra complexity adding more cost, more weight, decreased reliability, etc. Essentially companies are making a series of compromises to save space, weight, and cost. If the near-perfect folded design costs more to produce than Kawai's design, but saves weight and space, would they be able to profitably sell it in products at scale?
It just seems to me that the closer your design is mechanically to what you're trying to simulate, the easier it will be for that design to mimic all of the various little weights, inertial feel, frictions, etc. I think also a mechanical design that is more similar to the real thing will tend to stay more stable in maintaining all of those small differences over the long run than something that uses special grease or felt to mimic friction, etc.
I believe there is also a benefit in feel, but probably not in reliability, to using long wooden keysticks in terms of vibration transmission, weight, and maybe even other aspects.
Could an ideal folded action perfectly mimic all of those aspects? Sure, but if I were designing one the path I'd likely choose to take would be similar to Kawai's, if I was willing to take the size, weight, and cost penalties associated with it.