I agree with much of what you posted but not this. Kassian was far from perfect but I actually thought he played well. His puck protection stood out to me and even threw some hits for once.
It wasn't that he would have caught the player or stripped him, but he stopped skating and left room behind the offensive player which really limits the ways the Dman can angle player with the puck.
I'm going from memory but I'm 99% sure there was no trailer for him to pick up. A hard back-check likely results in the offensive player getting squeezed out along the boards and puck being pushed deep behind the net for a one on one with our other D against the 2nd forward. He didn't make a mistake (he didn't have a defined responsibility on that play)- he lazily passed up an opportunity.
He looks great along the boards - he made a great pass to Sestito for a shot off the halfboards. The issue is that he looks awful in open ice. He stops moving his feet way too quickly and he doesn't have near the acceleration to get away with doing that.
He seems to always be waiting for the play to be defined along the boards instead of actively finding ways to force the play there.
And Santorelli is amazing on the boards for his size. He's constantly winning puck battles. He's made some brilliant back checks so far this season too. If he and Schroeder can give us the roster flexibility to move Kesler to the wing at times, we're a much better team.