Not going to read the article, so you might not want to rad this post ....

Not many people I know are planted on the saddle when hitting bumps if they can help it.

A longer seat post can bend a little as a lever but how much? Not a whole lot, and even so, even with a slack angle, most of the force is down the tube ... saddle rails probably flex more in terms of actual measurable motion than the seat tube.

And I thought it was well understood that "frame material " pretty much is meaningless .... because "frame design" determines the properties of the frame, no matter its material.

I am sure the article does a good job of describing what their tests were designed to test. Not at all convinced it has much to do with how most people ride.