I personally don't see how this instanced striking dummy is different from SSS except some little adjustments. This dummy still means nothing in terms of being able to do the battle properly, because you know what?
Striking dummy and SSS do not teach you anything. It only checks if you are able to pass dps check in theory. That's all.
It's one thing to pass dps check on static doll that doesn't hit you and completely another to do your best with action happening around you with all Force Majeures as well (that do happen even in most good parties).
There is no way to prevent high end content from having unskilled players there, because not even the best simulator will teach you the real battle with 7 people beside you.