Back when the 2015's first came out, the vast majority of the automotive press preferred the V6 suspension over the V8 adjustable suspension. I think that if it has been discontinued on the V8, that is the reason why (and since it does cost more to provide it). Also, they need to have some features on the Equus (G90) that are not on the Genesis.
My impression reading the press was the same although in each case the V6 was preferred for being sportier, which the weight difference and electronic steering settings also contributes greatly. CDC tunes in stiffness in sport mode but more importantly, in every mode it continuously adapts to the road surface conditions, body roll etc to stabilize the ride experience: great for luxury cruising. IIRC, the Equus (non air) suspension was CDC.
edit: the 2015 has both air suspension and CDC shocks.