I could be mistaken, but I don't believe Nick was talking as much about chassis flex as he was chassis displacement. Think of it this way, if you roll over a speed bump at a crawl, the chassis displaces 100% of the speed bump height while the suspension effectively displaces 0% of the speed bump height. As the speed increases, the suspension displaces more and the chassis displaces less...To a point though, and it's not a direct correlation. Even the softest of suspensions cannot have the combination of suspension and chassis displacement be less than the height of the bump itself, and the stiffer the suspension the more chassis displacement biased it will be.
So the springs and dampers work in conjunction to naturally resist suspension motion and translate it to chassis motion. To illustrate just the damper part of the effect, look at my suspension displacement vs time plots in the linked thread and notice what happens to the suspension displacement when it goes from undamped to damped:
https://www.locostusa.com/forums/viewtopic.php?f=5&t=891&start=90As such, when combined with the spring effects, I would anticipate that on the vast majority of low slung sports cars, even on the more 'softly' sprung side, the suspension will typically still be stiff enough that the chassis will be displaced by bumps nearly as much as, if not more than, the suspension does.