Is true than the keys on the ydp 181 are not very responsive?
Is the source of this statement a competitor? James does well to point out that the difference between the models & actions, but the purpose of the third sensor ≠ added responsiveness in any general sense. In a specific sense, it allows you to replay a note without fully resetting the key. For a beginner, I see no benefit; for an intermediate player, someone would still have to explain the difference to them. For someone with advanced technique, there is clear benefit.
Generally speaking, a student is not going to learn advanced technique on a digital action, though they can reproduce it if they learn it first on a nice grand. That's the missing link in the chain for cost/benefit.
The 3rd sensor is a good thing, but Yamaha's GH action is proven, and in the most critical eyes, would be considered an above average digital piano action. My speculation is that the 3rd sensor may become a standard feature in Yamahas for competitive reasons in the next couple of years.
The CLP-430's has more powerful speakers & front legs on the cabinet to change the aesthetic. Those are benefits you can see and then compare for the price difference.