I 'd agree that the lack of real escapement in non-hybrids is the main issue here. Real escapement is theoretically not needed, because no physical strings would get muffled without it, but this doesn't mean all the properties without it are the same. The acoustic action with escapement is a "hybrid" (switching) mechanical system, and with double escapement a more complicated one.
I also very much agree with the two options
Use soft cushioning, so that there's not a lot of rebound oscillation but at the price of the bottom feeling mushy
Use hard cushioning to not have mushy feeling but then there will be a higher rebound
though I think some DP actions are reasonably okay for many people, not too much one or the other.
To work around the above, some pianos just lighten up the hammers, so that the entire action is light and thus will reduce both the rebound energy, as well as the pushback. That's usually Kawai.
I think this isn't a special Kawai thing. Almost all entry DPs have light hammers & low inertia, while most upmarket ones have heavier hammers with higher inertia. However, their properties regarding the rebound still differ, maybe because of different damping (cushioning), maybe due to geometry. The RHC has light hammers, but the RHIII doesn't.
I don't have much experience with the RHC, I just vaguely remember that the ES110 did seem quite bouncy. But when trying RHIII models it struck me that the ES8 (which I was interested in) was quite disturbingly bouncy on key return while the CN39 (which I was not) was not annoyingly bouncy at all. KJ at PW rather pulls jokes on me for repeating it at every (in)convenient occasion than providing a response that would be helpful for Kawai users annoyed by the bouncing. I also inquired by email at Kawai support at the time, but they responded with a high-speed camera proof that the CN did have a bit of a bounce too 🙂 Release notes of some recent models did mention unspecified action modifications regarding this, but that doesn't seem to stop users from complaining.
But I'm surprised that in the absence of love from Kawai support, the user base appears quite passive. For instance, I haven't seen anyone try to replace the hammer damping strips with a different material, maybe from another brand if the thickness is suitable.