Mike, the road shock does travel up the steer tube, but it also has force components perpendicular to the steer tube - the wheel can be knocked back and up or even forward and up. Then the fork flexes and rings due to the impact. The inital force is a sharp pulse, and the higher frequency ringing components of motion should be mainly transverse at least due to fork ringing. Some of this complex of energy is carried axially and transversely into the frame due to continuous headset bearing contact, and we can expect some new ringing to start at the frame/rider/loading resonant frequency, with damping so it tends to die out the high frequencies. Some goes into lifting the head tube which helps to lift your handlebars and the saddle. This all is much too complex to fully deal with in words. Perhaps they should flex as a result - both Nessism and I appreciate the comfort of an O/S thinwall frame like ELOS, and it has to have energy input from the fork. 853, also oversize and thinwall, should have similar characteristics.
It's also a physical reality that it's practically challenging to go much thinner than 0.4 mm without really exotic alloys like 953, and a double oversize has a rather higher 2nd moment than single oversize like ELOS so it is stiffer as long as it doesn't beer can. How much performance you get out of 2nd OS versus OS is certainly a complex question, and debatable. Damping can be provided by the tires, the tape, the saddle, and the rider, ignoring any racks or luggage. We all know softer tires give a ride that feels smoother, and that well-broken-in leather can feel softer to ride than say a Toupe without gel. The frame can reduce vibration but not convert the energy to heat, so it's technically not damping though it may improve the way the bike feels.
Any case, I think the frame has a lot to do with shock absorption at the handlebars. At least I think there are good reasons not to discount it.
However, I see you have by now bought tubes and are marching down your road. I wish I knew how to make a frame.