Creative Speculation

I think part of the problem is that, as we discussed before, it's hard to tell what he intends to argue. In his Balzac-Vitry analysis, he says that the top is accelerating at -8.5 m/s^2 initially, then at -2.1 m/s^2 for about 0.8 s "as the contact begins," then at +3.3 m/s^2 (deceleration relative to gravity) for about 0.4 s when the two sections "fully engage." Hmmmmm. Wow, that's facially weak. (Just what does Chandler think is happening for all that time between the beginning of contact and full engagement?) But anyway, I mention the numbers because I'm not sure what you have in mind by "about 2/3 g acceleration" -- maybe an average, maybe different demolitions.

I imagine Chandler would say that you completely missed his point: his argument that the structure below is only resisting a fraction of the weight of the falling structure (to paraphrase your paraphrase) applies unless the falling block "actually impacts" the structure below (around 2:05 in the NTA video) -- and we know that it didn't because of the (supposedly) uniform downward acceleration.

Of course, that raises the question what Chandler thinks is happening to provide that resistance. (IIRC, Bolo tried to get at that.) Hell, I'm not sure I can enumerate all the questions it raises.