I would bet that Mr Denney would be the first to tell you that he could not feel the difference between frame materials (all other things being identical).
Do note the choice of words: ‘perceived harshness…’.
If you are a proponent of the famous ‘sound transmission theory concerning carbon’ then you should explain how the high frequency roughness components (very low amplitude) get transmitted to the frame through tires, rims, spokes, hubs, then through the frame, and then back to the rider either through: 1) bottom bracket, pedals, cleats, shoe sole, sock 2) seat post, saddle rail, plastic or carbon of the saddle, leather or synthetic cover, cycling shorts or 3) fork, stem, handlebars, tape, gloves.
And it should be very easy to measure it all, since the difference is so obvious.
When someone shells out 3000$+ for a carbon frame because he thinks it gives a smoother ride, he will feel it.
Francois in Montreal.