My opinion is that many Genesis buyers want the V6 models due to it being a better value overall in-terms of fuel economy and affordable luxury. The V8 models especially the R-spec is nice on paper, but many people do not actually want or need the extra power and handling. Therefore, not many R-spec were made or purchased in relation to the other Genesis models. R-specs are very rare and will be collector car I bet in the future in the Asian car category.
The same could be said of the 2015 Genesis Ultimate models, most used 2015 V8 models available in my area are the non-Ultimate models which does not have the active suspension and HUD. The rest are usually 3.8 models. However, you cannot tell the different in V8 models on the road unless you sit in one due to both V8 model having the same wheels and 5.0
badges. The only other way to tell without sitting in a 2015 model is to look thru the window at the info screen size(ultimate has a bigger screen) and check to see if one has the rotary info control knob which would make it a Ultimate model.
I have seen only one R-spec in my area on the road based on the wheels and
badge. Those car are very rare.