So are you saying that the point of the aiki taiso is to learn how to apply shear to someone else's structure? Or does this way of moving also strengthen one's own structure against shear?
Both. The trick is to move the effective fulcrums around in a persons body. Sometimes their body "cooperates" reflexively from a pulse of proper shaped/rhythm suddenly shifitng the "center" or effective fulcurm deeply into their body before they can act to oppose its shift. The "head-pop" trick from "jerking" the arm is of this nature.
Sometimes one can (as in kokyu tanden ho) find the "thin end of the wedge" in a very slight shear at the connection and then steadily propagate that shear moving the poised moments defining the effective"fulcrum" further and further into the structure (becoming progressively more difficult to oppose with levered power (because the effective "lever" arm on their end is getting progressively shorter.) Theya re the same, only the latter allows the conscious and subconcsious mind to both to perceive what is occurring structurally, and to better coordinate their rather different forms of learning . That learning allows one steadily learn to better "catch" and "throw back" if you will, the shifting shear center being thrown one's way.