I’m with you on this…as far as rear-end stiffness is concerned. Front end stiffness can be discerned pretty easily by just twisting the bike a bit while stationary.
That said, I kinda get what he’s saying…some of the front ends of these bikes just don’t seem stiff enough at all. The aerobars on the 3T cockpits don’t seem stiff at all–all it takes is a two-finger squeeze to get them to budge a significant amount. After watching one of the protour riders snap an aerobar during the TT in the TDF I have to wonder whether a more expensive, feathery-light cockpit would stand up to heavy duty daily riding.